BTW - Look at the 929 frame sometime. The swingarm attaches to the motor which is used as a stressed member and bolted to the frame. The F4 uses the conventional way of having the swingarm bolted to the frame and the motor is just hung in there. You'd have to chop the hell out of the F4 frame to get it in there at all since it is probably quite a bit wider (plus the whole swingarm attachment deal). Then you'd have to worry about the rear shock attachment since that would be totally different.

You could try to get a 900RR motor in there. Many people have done the swap with F3's which is very similar to the F4.