GM parts are all stamped and can be identified by looking up various identification numbers. You'll want to start with your owner's manual, which may have some of the numbers you need.
Check the block casting numbers. These are found on the driver's side of the engine, at the back of the head on the transmission mounting flange. You can use a mirror to see it, but it's more noticeable during a dismount.
Compare these numbers to the small-block ID numbers provided by the manufacturer to determine engine bore size and main cap.
Determine the size and appropriateness of your engine for your build project based on the recommendations in the vehicle manufacturer's guide.
If all else fails, you can always take the engine to a machine shop to get an estimate of the engine's power and weight ratios. A good machine shop can give you a quote on what it takes to rebore an engine, assuming you want to do a rebuild.
