Here is what you need to do!
http://www.fiero.nl/forum/Forum2/HTML/065545.html
I thought about doing something simillar, I was thinking of flipping them so I would get the real look of a v8, Link them both to some sort of frame, have a shaft passing in the middle of both, each engine would be connected to the shaft by a chain, you could then connect the shaft to a normal transmission. That would take a lot of fabrication. This guy did it much more simply althout I dont know how the transmission are holding up. If you want even more of an exotic sound take two of those, http://cgi.ebay.ca/Arctic-Cat-1000-Triple-Engine-Complete-Thundercat_W0QQitemZ220217100007QQihZ012QQcategoryZ100468QQrdZ1QQssPageNameZWD1VQQ_trksidZp1638.m118.l1247QQcmdZViewItem put a chopper style belt on each end, with a shaft in the middle as I said, would be even simpler, and it would sound really brutal. But would probably be a brute to drive, giving the power curve of most two strokes, which would make it even cooler!