How to Finish Bill Wirges' Last Project Bike?

More than a few years ago I bought Bill Wirges' last project bike, a Kawasaki chassis. He was quite old and ailing with health issues and it was hard to communicate. I bought the bike and some other stuff from him (missed the Bonneville streamliner) and brought it home. My plan is to make a plan and finish it next Winter. I have a 1975 Z1 engine.
Can anyone tell me what tank and tail combo will work on this chassis? Will the Z1R tin and plastic fit on this frame? Any suggestions welcome. Bill built an entire stock appearing exhaust system with race-style baffles for it. It's quite amazing.
Any suggestions welcome. TIA
 

Do you know what year the frame is?  Does it still have a serial number stamp on the head tube?

If it's a Z1/KZ900/KZ1000 from '73 to '80, the Z1R tank will likely fit on fine.  The Z1R seat mount is different from most of the other models, and the rear tail cowl mount is also different.  But if you are determined it could be adapted.  The side covers also have a different tab location, but it looks like those have already been adapted.