Help! Engine Swap on KZ750H1 Frame

I've got a KZ750 E engine in my H LTD model frame, but it's been taken care of just as horribly as I'm certain the original motor was. I'm in the midst of a rebuild but I have a couple other engines in my shop. I'm wondering what, if any, engines will sit in a KZ 750 frame without much in the way of extra fabrication outside of fashioning new mounting brackets. I'd rather not weld onto my frame, as it's been freshly powder coated. I have a KZ1000 engine but I'm uncertain it will mount properly. Does anyone have any insider tips? Maybe bobber builders or cafe racers who have gone through a motor or two in their day?

I'm sure this will be sacrilegious, but I DO have a CB900 and a Suzuki GS750 engine...

The 750 was born by boring out the 650 and it shares many of the same attributes. I seriously doubt you will get any of the hulking sized engines you mention to fit in the frame without major surgery.