Re: 302 or 351
Dmax is right, only way to tell for sure is to measure the stroke
Engine codes/numbers will tell you what the car left the factory as, but after 25years things more than likely have changed
I've never had to do it myself, but this is it in theory
*remove a spark plug
*use a pencil or similar (some just use the dipstick) and feed it carefully into the cylinder, making sure the piston is at BDC and mark the pencil/dipstick/dowel whatever, at the spark plug hole.
*rotate the motor by hand until the the piston reaches TDC, mark the rod at same point.
*remove rod and measure the distance between the 2 marks
3.5inches = 351
3.0inches = 302
it wont be spot on those measurements, but close enough is all you need to tell
hope that helps, good luck