Ford Engine size

Rancher,
The easiest way I can think of for you to identify difference would be to take some physical measurements. Grab your trusty tape measure and measure the distance between the crankshaft snout (balancer bolt) and the DECK of the block (where the head gasket is). Now, you'll have to kind of hold the tape measure out a bit, but if it reads close to 8.2 inches, you've got yourself a 289 or 302. If it measures close to 9.5 inches, you've got a 351 Windsor. What may even be easier would be measuring the distance between both front intake manifold bolts of a known 302 and comparing to the motor in question. The 351 Windsor uses a wider intake due to the taller deck height. Best I can offer.

An excellent recommendation-I DITTO IT.

the firing order will be different than the 302 also

302 or 351?

The two easieast ways to check is to look at the thermostat housing. If the lower bolt is behind the water pump then its a small block. If you can reach the lower housing bolt with out going behind the water pump, its a 351. Another thing to look at is the timing cover. If the top of the block is flush with the top of the water ports going through the timing cover, its a small block. If the deck of the block is about 1 1/2 inches above the timing cover, its a 351.