Tucker bought out the Franklin aircraft engine company and had one of
their airplane engines converted to watercooled. For those that don't
know the Tucker had a rear engine water cooled boxer 4, but the early
prototypes were aircooled.

I'm not sure what happened to the Franklin company. I know they were
sold off after Tucker went broke.

A 2.2 or 2.5 Subaru is going to give the most bang for the buck in a VW
based dune buggy. All the adapters are all off the shelf items and the
engines are commonly available.

Tony