I'll do some measurements, if feasible will obtain another frame for the project Might even bolt up to the stock driveshaft. Of course the lower fairing will have to go. GPz1300
Be realistic. You'd go through all that work to make a bike that will handle poorly and be slower than a stock Kawasaki GPz 900 from the Reagan era.
If you don't have fabrication and welding skills, do yourself a favor and get rid of it.
It's not worth risking being in a wheelchair or having a limp for the rest of your life to ride the stupid thing.
Let me think; project must be unique, take up all your time and money, and will kill you.
I'm thinking homebuilt aircraft. Maybe a replica of the GeeBee. That thing killed almost every pilot that ever flew it. (Engine shape is wrong, though.)
What about finding a KZ 1300 that needs an engine? Seems the best purpose for that engine is in the bike.
With that said, lumberjack competitions just might be making a comeback as the most popular sport in the United States during these trying times. You would clean up with that thing swinging a big blade!