If you bolt the motor mounts from the B18 onto the B20 and keep the breather box
that came with the B20 everything else should fit OK. There are a few very minor
differences but nothing that a little judicious selection of parts won't overcome.
If the B20 had fuel injection that is even better - just plug the ports in the
head with 7/8" soft plugs (available for less than a dollar apiece at most parts
houses) and bolt up the manifolds from the B18. If you can use an exhaust manifold
with dual downpipes, so much the better.
Keep us posted on how the project goes!
--
George Downs, Bartlesville, Heart of the USA!