Allen Millyard in the U.K. has been building "multiples" of standard bikes for years. He was the first to turn a Kawasaki KZ1300 into a V12. He made a V8 Z-1 and several different Triple modifications. Mind-boggling talent.
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The guy with the CBX 12, Andreas Georgeades, also built a bike with a Ferrari V8 motor. His creations are a tad less practical in terms of "runnability" or rideability than Millyard's.