what do i need to look for to tell if its a 305 or 350 othere than opening it up

the best way is to check the casting number on the back lip of the engine. its on the drivers side. its close to where the tranny bolts to the engine. depending on what year the engine is it can be any number combination. 3970010 is the casting of a 350 for example. once you find the number go to here. http://www.nastyz28.com/sbchevy/sblock.html. it might be covered in oil so use brake cleaner. that worked the best for me. hope this helps