What a nice looking car!!
Bill (fwillyj) is correct. It is basically an "Iron Duke"/Tech IV/ SD Pontiac 4cyl. ( not the same as the old Chevy II thought similar) You recall Pontiac did have a SD block for a while and promoted it in several race series in the 80's. DOHC etc put that engine out of business and GM no longer manufactures it. Kansas Racing Products (KRP) has the rights and casts a new block with upgrades even over the SD block. Any SBC, and some Ford/Mopar heads can be made to fit and they have part numbers so engines so configured can run in make specific classes. I know a number of people using the block/engine combo in Comp Eliminator racing and they are still used I understand in midgets and were also an ARCA truck engine before they went V-6.
My engine is debored (from factory, didn't sleeve it) to 3.875 (normal is 4") and with 2.58 stroke for 121.7ci. It has a SBC head with custom intake for injection made by a guy who races similar in Comp eliminator. I know of an engine in a comp car with 202" made 465@9500 on dyno with a single carb so they can be bored/stroked a fair amount and the block is strong.
Having run Cosworth Vegas for years at Bonneville, this engine was a step back technology wise (pushrod engine) It is stronger and makes more power. Folks had suggested I just put a Honda in it but that offended my tender sensibilities and I wanted a different direction so this is what I did. Considered the Ecotec and we have seen Ron Main and the GM Cobalts do well with that engine on the Salt.
Jack