Chevy V8 is not expensive to tune at all, steel crank, steel rods and forged pistons for well under 2k from the states ! still think there would be too much low down torque though which is why the bike engines work so well as they have very little torques

Hot pinto would be a good starter though and still bloody mental, why not just spend 4k on a Alloy cossy block to keep the weight down whilst your at it

Proper cars though but horrible for anything but track days and a bit of a sunday burnup