If I was going for a transplant I would go for a Suzuki Hayabusa engine. The modified Hayabusa powertecengineering.com were manufacturing. A V8 (2 engines mated on a common block) pumping out 380HP with a redline beyond 10k. And it looks so light!

Thats what goes in the Radical SR8. Makes a seriously impressive package in there 
you won't get change from £10,000 just for the bare block, plus another £5000 for a gearbox for that you don't get a reverse either.
my choice will be to go viking power, around 600bhp

Yup, it is a expensive piece of custom engineering OK. Not all is lost.
BGH Geartech have the technology for a DIY shaft conversion, onto the standard bike gearbox. From what I've been told the standard Hayabusa gearbox can take a severe amount of trashing built to handle high levels of frequent power and torque. On a acceptable conversion budget you are back to 4 cylinder power but keep in mind the 4 in-line version Hayabusa can be tuned up into the 300 bhp bracket and it's power to weigh ratio is excellent. The crux of the problem is the introduction of a differential (rear axle) to feed power from the engine final drive to left and right axles. Is there room for one and if so how to configure the final drive, diff, shafts with good engine placement? Here's a Hayabusa in a Fury chassis.
Reverse ain't a problem, it can be supplied via a electric motor.... unless of course you race in reverse
I reckon a Hayabusa conversion could have a good chance of success in a VX. Image the fun of screaming around the track with a perky engine on a red-line of 10500RPM+.
Edited by speedster, 01 October 2010 - 01:54 AM.