I've never heard of a shaft-to-chain conversion on a 750, but I'd guess it's possible since it has been done on the 1000s.
It's going to take quite a bit of work as I'm pretty sure you'll have to split the crankcase.
Here are a couple of topics. google search = kz1000 shaft drive chain conversion. you can try other searches.
KZRider topic --- 1979 KZ1000 shaft to chain conversion --- by SpikeJ
This is an old topic. he mentions a photo blog that might still be floating around the internet somewhere.
custom fighters --- SpikeJ topic --- see reply by Mustapha-dump
He provides some of the particulars.
Forks. search KZR for
KZ750 fork swap or something like that. All-Balls-Racing has a cross-reference for figuring out what fits what. Basically, there have to be bearings that will mate the donor steering stem to your frame, then have the steering stem machined --- I guess cut to the correct length, then the end re-machined or something like that.
Rear end. do a KZR search for KZ750 swing arm swap.