From the Olds FAQ (
http://www.inil.com/users/dlbrown/oldsfaq.htm)...
"Small blocks from 1977 onward will have the CID or liters cast in large numbers right above the center core plug. The engine VIN number will also be cast onto the side of the block."
"Facing the front of the engine, at the top surface of the timing chain area, to the left of the oil fill tube, there is a code about 1.5" high followed by the casting number. A letter indicates a big block, a number indicates a small block."
There's a list of casting numbers and associated displacements at the Olds site mentioned, along with pretty much ANYTHING you want to know about these engines.
As for properly mounting the engine, the frame brackets and motor mounts from a 403 equipped '77 to '79 T/A should work easily.