Racer; I shall be very interested to see whether you really have cracked the problems of rubber-mounting an engine in a rigid frame (although I'm now confused with the talk of using 'Busa suspension...?)
I've probably spent as much time working with rubbermounts as anybody; and I've not come across a setup which works well.
Obviously, as others have mentioned, if you rubber mount a chain/belt drive engine & trans in a frame without rear suspension, then as soon as you apply power, the drivetrain will pull itself backwards to the full extent that the rubbers will distend. The chain then comes off.
So; you introduce some means of stopping the engine moving back. Tie-rods etc. Trouble is, you then transmit all the horizontal vibrations into the frame but none of the vertical ones. As most engines vibrate in an elliptical motion, this ellipse is cut into jagged zig-zags.
The result is a much nastier vibration than would have happened with a solidly mounted engine. Cant keep feet on pegs, extremities (like light lenses) shattering. I once saw a license plate moving back & forth about 2 inches, when you could only flex it about a half inch by hand...
So, as I say, If you've avoided these pitfalls, I'll be very impressed.