A piston engine is an air pump. Perhaps you could take a well worn one that is worn eveny and add spark plugs and a carburator. I don't know how you would mount the distributor though. In the end you would be cheaper to just buy a good used engine even if it were a gasser.

The old 5.7 olds diesels were so similar to the gas engines you could bolt on gasser heads pull the injection pump and install a distributor there and run them as gassers using the stock diesel cams. I hear they put out a lot of power too.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.