You're thinking condensor, not radiator, though they serve basically the same function. Any aftermarket company like I.C.E. that sells complete kits for the Bug motors will already have a sized condensor for the kit. If you're going to patch one together from junkyard parts, I think any unit from a small car like a Cooper, Smart, or something like that would be more than adequate. Too large a unit and the A/C won't cool as effectively, so buy wisely.