What you have is a mishmash of a 140 and 240.
Fiber glass is another way to do it, but the rust eventually comes back.
The comb b21 head with a b20 bottom sounds funky. Thanks for the great advice Ray, I went and looked at the car more closely today. Everything on the top of the engine is from a 240 it seems - fuel injection, power steering. The body work is very well done, with no bubble rust or waves in the body. It certainly isn't an original 1972 since he has even replaced the back windscreen with a 240 one.