Re: 900RR in a 600RR FRAME?
Check local motorcycle wrecking yards for a 900rr bike that you can fix up, maybe put your 900rr engine into it if needed. I called my local bike wrecker about 6 months ago and he said he had a complete 900rr he would sell me for $1000. It needed some work but it was all there. You may even be able to work out a trade for your engine towards another bike from the wrecker.
The 900rr engine is going to be wider than a 600rr engine. so making it fit may be a real pain in the butt.