Decode the engine. Your inline six will have a casting code near the dipstick. I’m fairly sure the 250ci wasn’t introduced until 1966. A 230 & 250 look the same externally, so you can check the top of the piston with a feeler through the spark plug hole. The engine will also have a serial number stamped on the pad next to the distributor.
Check the location of the lower radiator saddles. The inline six will have the lower saddles riveted to the lower flange of the crossmember. A V8 would have saddles riveted to the upper flange of the crossmember. An inline six would have a taller narrow radiator. The V8 used a wide but shorter radiator.
