If cylinder is good, you are GOLDEN, just use 750 big pin cases (almost identical to SXR) and an SBT crank and get a new top end. The cylinder is the KEY to having Kawi power. 750s are DOGS due to poor port timing. They would barely push an SXR. The 800 porting makes all the difference.
So carbs and everything are good? If so, you could get it going for about 1000. Used 750 cases $100. SBT crank $250. Top end $300. Ready to roll. The cylinder would be the expensive part, but I would NOT cheap out and get a 750. You will HATE it.
Post pics of all engine parts and we can help you out.