You need to talk to Hot Rod Lincoln about the Pontiac OHC six. I had a general repair shop in the 60's and several customers had the Pontiac Sprint which was the the 4bbl version. They had their share of problems. We have a customer with a 54 that has the GM 4.2 Vortec or "Atlas" dohc I6 that is a real tire smoker, gets 23mpg, and are pretty much trouble free. They're getting reasonable in price at the salvage yards.
