To Mod or to not Mod my 1981 GPZ550

I've been kicking this project around for too long now...everything is ready to come back together, but I just can't decide on what to do as far as modding it.
Options:

1.  Restored back to original condition no mods to engine other than rebuild with new parts, mild suspension upgrades, cartridge emulators and KYB ZRX shocks.

2. Restore cosmetically but mod the engine for more HP.

3. Full resto-mod with upgraded parts, including suspension, swingarm, wheels, engine, etc...

4. Restore same as three except swap the engine out for a 1986 ZX600R Ninja liquid cooled engine. 

Most of the restore work is done, parts, frame coated, original engine ready to be assembled in stock form. 

In my research for a option 2,3 I have found the parts needed for the HP upgrade.  They are 26mm CR carbs, 615cc big bore, Dyna2000 ignition, Kerker 4into1, head rebuild and port and polish, & Megacycle cams.  This is probably good for 10 to 15 HP bump..I hope...this is the most expensive route. $2500.00+

For option 4, I already bought all of the parts for the most part(cheap).  Engine was dirt cheap but needs a complete overhaul.  Not all of the engineering has been completed but it is possible.  HP, according to the specs is 85HP at the crank.  I might be able to get 65hp from the stock engine, so this is a big jump.  However, this is the longest route as the engine needs rebuilding, parts fabricated and fitted....etc....and I want to get it going by fall. 

What I'm thinking is Option #1 to get it going and work towards Option #4 using a donor cheap dog frame for the fabrication.  If I can get it all fitted, then invest in rebuilding the ZX600R engine. 

Not sure if anybody has gone these routes before, if so any advice is welcomed.

Almost forgot...original bike was bought as a rescue for $300.00 barely running.

Thanks
577Nitro

Does anybody know if there exist a form of a Rosetta Stone for the (GPZ) 550 engine form factor?  What I want to know, and I think Corey is the man, is what late model top end parts fit on the other early models?  IE: What is the difference between the 84/85 heads verses the 81>>83 heads? 

Is it worth swapping top ends?

577nitro

1981 GPz550s are special. I wouldn't do anything that can't be reversed unless it's entirely internal. 

My $.02: keep it stock, or maybe a mild resto-mod with period-correct parts - changes that can easily be reversed.

There aren't a lot of '81 GPz550s. You could mod the heck out of another bike that isn't as rare.

Also, check partzilla.com for part numbers and compatibility/cross-references.

I agree with the others.  Dumping a bunch of money into the bike to make it perform better makes little sense when no amount of money will make that bike perform better than something like a 34 year old Honda Hurricane.  

No matter what you do to it, a CBR600F1 (early model) will run rings around it.
So, unless you're talking it to vintage track days and such, is there really any point to things like cartridge emulators? The sky's the limit on what you can spend on a bike. However, a future buyer will probably value originality more than whatever mods you've done. The GPZ600R engine swap is possible but may even harm the resale value. And the resale value does matter, because, even though I'm making an assumption here, you seem to be a technical type who prefers to get hands-on with tools than just ride around for the heck of it. How many miles is it really going to get once complete? Not many, right. So leave it stock.

Seriously? 
Keep it as original as possible! 
They  are "one year wonders".
The more original you keep it the more it will be worth when it turns 50!
 They are extremely rare already!

H.

Welp...stock it is...with SOME suspension mods for safety.   I have the cartridge emulators, racetek springs, fork brace, and Zephyr KYB shocks.   I do have an original set of low mileage stock shocks with the 5 position compression still working fine...those are for show.

Thanks for the input...I had been leaning that way, and this just confirms it.

577nitro

you can never go wrong with smart suspension upgrades... and the best tires you can afford.
 

I’d vote for option 2 - keep it stock cosmetically but put a little more pep in the engine with something like a wiseco 615cc + free flowing exhaust + cams upgrade. If it needs engine work that is…otherwise just ride and enjoy.