Ok, here goes:
1. Missing exhaust system
2. Missing spark plug #4, what about others?
3. Missing right driver foot peg
4. Appears to be missing carb boots that go between the carbs and box. Is the airbox present?
Now, let me say that I have ridden an '82 KZ1000 for many miles and in fact that was my first bike. I like them. But I would be very cautious about that one. Toilet paper stuffed in the spark plug holes and exhaust ports may not be the best way to keep water out of the engine, ha ha!. Seriously, anyone that leaves a bike sitting without a plug in the spark plug holes probably has done other unexpected and potentially disastrous things to the bike. If it is under a shed that helps, but who knows if it was only recently pushed there.
Check for any and all missing or damaged parts and consider the replacement cost. Don't get emotional and approach it with the expectation of having to to rebuild the engine. Is the other engine known to be good?
You could be looking at quite a bit of money to get your 90 hp back unless you know something about the bike's condition firsthand.
Best of luck!