You don't have to break the bank on a MegaBusa build.
If you are looking for a Bike kit there are kits out there that are a lot less expensive that the Westfield. ... My DeMan Busa SR7 sure was.
If you have the chassis already the simplest way to convert is to measure the bottom mount points for the bike engine (have a solid mount plate welded to accomodate it...bolt or weld the plate to the lower rails of the bix tube), measure the top mount points (have a cradle welded that will bolt to mounting points on the top rail of the box tube), buy a "bike flange" (to match the output shaft of the bike engine to a drive shaft...I think you can get a universal shaft from Rocket), buy or have made a prop shaft that works in your car, then do all the connections.
Cable works well for my shifter...theres not much rocket science there.
Then there's the issue of the wiring harness. ... Most locosters use the bike loom and adapt it for car use...mine works fine.
Good luck!
PS I have found that the Locosters in the UK are about a light year ahead of the curve on this topic and you would be well advised to visit ...
http://www.locostbuilders.co.uk ... often!