Here's a related question: Has anyone ever gotten two SOHC 4 CB500 engines in a single frame?? Saw off the 1st trans; chain (or gear) the engines together; and run it??
I know it's been done with older (pre-unit) BSA's and Triumphs, and just about any Norton...but a Honda SOHC Eight...Wow... 
I have seen cb engines with the trans sawed off for other applications where a pripary was used with another trans.
If one had access to a machine shop, theoritically you could build a v-8 block (using a shared crank, maybe even v shaped con rods). theoritcally bothe banks of cylinders would have to have their own igniton and valve timing. Allen Milyard and Simon Whitlock in england have managed to turn 3 cylinder kawasaki two strokes into 4, 5, and even 48 cylinder engines. Ideally they use two strokes because they don't have to mess with cams. What is nice about their creations is that they fit in the frames and look stock, where as you could not do that with 2 cb engines or a v-8 engine.
Not that the cb750 frame is that great and all, but I would like to someday see someone put a cbr 1000 engine in a k0 frame. I have seen fzr600 engines in a lot of older super bikes (including a kawasaki h1) why not one of these new modern marvels. On second though a cbr600 motor would be fine and you could run the F3 wheels.
