The drum frame has the hole for the rear brake pivot point that converts the brake pedal movement to the brake drum lever movement.
Rear disc frame doesn't have this, it has fixings for the rear brake master cylinder. Disc swingarm is also different.
So wouldn't be a straight swop.
Z1000 rear disc.

Z650 rear drum.

What's you use plan? Drag? Cruise? High Speed? Or just to be COOL at cruise night?
Budget dictates it all of course!
Don't go too long!
Try the old Suzuki GS conversion. 160-180 tire is pushing it.
For wide. And cheap, the Kaw ZZX 600? 2004-7. Thee parts are cheap on ebay. Really easy to convert, for 2 shocks like stock
Or have custom built to your specs by "PDM"
Your opening up the worm can / rabbit hole! offsets, frame mods, etc..
Keep an offset of 5/8" at engine.
Good Luck.
Here are a few things I did over the past 10 yrs.

NewYorKZ440 wrote: .................... whats the point in just struts then, like why even bother as manufacturer ? just cheaper ?

I don't think any motorcycle manufacturer ever used struts rather than shocks. I suspect some folks use them instead of shocks because they then can mount the rear wheel very close to the fender and frame since the rear wheel will not move up and down inside the fender or frame. Of course, one big problem with struts is the fact that when going over a bump or pothole the hole bike will jump up and down rather than just the rear swingarm, and this can lead to a serious handling problem especially if hitting the bump or hole while riding around a turn. The other problem is the fact that the jolt from any bump will be transferred to the rider, so some folks using struts mount the seat on springs. If you take a look at the seat in the picture of struts I provided you will see it has springs under it. Ed

I did do a search thanks, and have seen the attached thread before, but thank you for your time, although a little sarcastic.

My main issue is how to fit the swing arm into the frame as it’s width is larger. It’s only a few mm, so was looking at the different options and what bushing/seals are actually required. The pivot pin/spindle and sleeve from the kz750 could be used with replacement bearings with the required 22mm ID

Cheers jim

Partzilla shows the same part number on the 1982 GS1000S, 1982-1983 GS1100E, GS1100ES, and the 1983 GS750S.

Make that 1980 - 1983 GS1100E.

82 Suzuki GS1100E swingarm, got one on all my KZ's. It's a nice and easy upgrade. The only issue using them is you need different shocks with a clevis on the bottom instead of eyelets.

Suzuki GS1000. It was a popular modification back in the day. I have one myself. It is lighter than the KZ swing arm. If you decide to use it, you will need to use shocks for the GS or have KZ style lower mounts installed. You will also likely need a thin shim on each side of the pivot.

All your input its been very valuable its not the same to build a stock engine as building a HP engine, its tricky enough doing it from scratch but taking over an engine that someone else did its a different matter.
I took everything apart and I am getting c=the cases welded, then I am going to source the parts for that engine the pistons are not longer made from MTC and the rings are worn so either I go 1427 or do have custom made a set of 4 pistons and rings so I do not bore again the cylinder that will cause more heath. or high drop it to 1325I have recently acquired a z1900 engine that was set for 1200 and it has 125 psi I all 4 cylinder I am going to take the chance to fit it in the chassis and do all the prep to fire it that was I can asses any repairs needed and then I am going to fit a 1978 kz 1000 engine completely stock that I have and already did everything oem for this bike.
I am going to use to 1400 engine for a pro street build I am doing with extended swing arm and modern front end,
I keep you guys posted.

I'm looking for ideas on a wheel upgrade for my 79 KZ1000 MKII. I currently have a 3.5" x 18 front and a 5.5" x 17 rear. Both are stock KZ wheels that were widened. The front was an 18" from a Z1-R and the rear was a 16" LTD wheel that was widened and the diameter increased to 17". I had these done about 10 years ago and went with the 17" for a better choice of tires. I've never truly been happy with the look of the 17" rear wheel. I think it looks too small. I'll attach a pic below.

Fast forward to today and I'm planning to change things up a bit with a new, stock length swingarm and more of a sportbike style rather than the dragbike style I have now. It would be so expensive to have another wheel widened and chrome plated to match the front, so what are some other options? Modern sportbike wheels look nice but I don't want to change the forks and I want to keep the stock speedo drive etc.... I want to continue to run a 180/55 on the rear.....any ideas? Thanks