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Hi there; unfortunately it seems the output shafts are different between the chain and shaft driven engines, so to switch you would need to split the case of the shaft engine and replace it. 

Splitting the engine is not very complicated, but is pretty tedious in terms of scraping gasket surfaces for reassembly. 

I have a 1983 550 transmission for chain drive that I won't be using; if you want it it's yours for the cost of shipping.

I have the same motor in my KZ650 (1982 KZ750 Spectre)
To convert to chain drive I used the complete transmission out of a 1978 B model (had a spare hanging around) I split the cases to replace the transmission and remove the 750 shaft drive trans.
I first thought I only needed the output shaft gear set out of the 650, but I checked the gearing on the 750 shaft drive trans and it showed too much of a tooth difference to make it possible to only use the output gear set by it self. My calculations showed a massive tooth differential on the final gear set. The shaft drive requires the gears on the output to be rather high, possibly because of the bevel gear and the small cruiser wheel setup.

I had no issue using the complete chain drive trans out of the 650, I figure the 750/GPZ chain drive trans would be similar. I am using 17T front and a 38T rear on that set up and can cruise at 4000RPM at 65MPH.

Its too bad your 6 speed conversion did not work. Is your main goal to convert to a chain drive?

When I was looking at used 750 Spectre parts I knew the motor was just slightly off GPZ spec at a much lower cost. The guy selling the motor I eventually bought was also selling the complete shaft drive and rear wheel. I wanted to put that equipment in my 650 frame but I soon discovered the Spectre frame is over 2" wider than the 650 frame at the down tubes just after the output shaft. So my thoughts of having a smaller lighter shaft drive touring bike were dashed.

I did end up buying the Spectre motor plus a spare head/barrel/pistons because it was a bargain price. I really like the Spectre motor, its pretty strong and I like the fact that its not got the black GPZ coating.
 

wrote:

Picked up the seat Moose1800 was selling; thought there was a chance I'd be able to make it work, but no dice. I'll sell it along for what I paid at some point. Once I'm more sure what's what I plan on selling or giving away some extra stuff I've got. 

Sorry to hear the seat didn't work out for you, it is after all a seat for a KZ LTD if I were you I would put it on ebay for $125.00 plus shipping and break even on what you paid . It's in good shape and I don't think you would lose money.

wrote:

Its too bad your 6 speed conversion did not work. Is your main goal to convert to a chain drive?

When I was looking at used 750 Spectre parts I knew the motor was just slightly off GPZ spec at a much lower cost. The guy selling the motor I eventually bought was also selling the complete shaft drive and rear wheel. I wanted to put that equipment in my 650 frame but I soon discovered the Spectre frame is over 2" wider than the 650 frame at the down tubes just after the output shaft. So my thoughts of having a smaller lighter shaft drive touring bike were dashed.

I did end up buying the Spectre motor plus a spare head/barrel/pistons because it was a bargain price. I really like the Spectre motor, its pretty strong and I like the fact that its not got the black GPZ coating.

Actually the conversion is a success! The cases are together and all six gears work. I bought a 550 shaft transmission many months ago to check the fit in my spare engine, but it didn't have the forks/drum/etc; the cheapest way to get those was to buy a complete set including the transmission for a chain drive, so I was planning on just giving that away. I like having a shaft drive bike. 

Moose - not a bad idea, I'll think it over. 

Oh, Sorry I miss understood what you were trying to do.

When you said you have a 550 trans spare I thought it did not work.

So now you have a 6 speed shaft drive, I don't think many people have ever done that, maybe your the first!

Made a little tangible progress - after spending nearly 5 hours in total scraping with razors I decided to buy a chisel, which made short work of the remaining half of the gasket. Still need to be careful not to gouge, but I've got some woodworking experience. I'm relieved to be done with this part!
Afterwards I torqued down the oil pan and bevel gear unit; clutch isn't torqued yet, I only have red Loctite and I'd like to be kinder to my future self than that. 
I bolted awake this morning and immediately remembered that I forgot to torque down the spring-loaded shift drum bolt, so I'm kicking myself for reinstalling the engine into the frame. I get a little excited during this phase of rebuilds. 

Z1Enterprises and other places I'm sure sell scrapers to remove gaskets.
I find they work really well.
Come in different widths:

Gasket Scraper - 15mm | Kawasaki and Suzuki Motorcycle Parts | Z1 Enterprises

Gasket scraper or wood chisel. Same as six of one, half dozen of the other.

 

Was just about ready to put the clutch cover on when I discovered that I'm missing the dowel pins. Probably explains some of the past oil leakage...anyway, hoping I can find a part number for that instead of guessing. 

Cylinders honed, pistons soaking in carb dip. Shouldn't be too long now. 

EDIT: 92042-007 for the pins...I just remembered that I've got a couple that are longer stashed away, so if the measurements check out I'll cut those down instead. 

Little bit of progress; my girlfriend helped clean up the head, and I'm halfway done lapping the valves. I have the cylinders honed now, and the pistons nice and clean from soaking in carb dip. 

As I was about to put the new rings on, I noticed something strange - they didn't fit! Turns out my bike has different rings than some other 1982 750-4s. Correct ones ordered, so I suppose I have time for more cleaning. If anyone wants an unused set of Cruzinimage piston rings for the cost of shipping, hit me up. 
 

I was pretty excited to finally get it running again, mainly because I used my Ninja for deliveries last week and my back is on fire. Oh well. 

I slacked a lot waiting for the correct rings to arrive, so to make up for that I spent about 3 hours on the bike today. All rings measured .38mm gap on each cylinder, so I'm confident that - barring any possible ovaling, I didn't bother checking - my engine should be just fine. It's got maybe 30k on it by now, so I think much of my poor performance was the very glazed cylinders.

I decided to try this approach to installing it all:
Don't do this. It would be so much easier to just slide the cylinders over the pistons after installing the wrist pins, and even moreso if you have the right tools. Lesson learned I suppose. 

I mentioned earlier that I was "definitely" painting the cylinders, but I changed my mind when gas shot up. As previously mentioned, I spend a lot on gas for work, so the KZ would help a lot with that. 

I don't feel like looking at a wrench for a month after that debacle, but head work is easy and I'm about to start reviving my late grandfather's GL1000 (now my cousin's), so I'll do my best.