What are the obvious visual differences between a 302 and a 351w?

 

351w is taller and wider....more displacement....i dono about bores but id assume its bigger....

 

The top of the water pump flange is flush with the deck on the block on a 302 & on a 351 the deck is about 1 inch above the water pump flange.

 

They do look very similar. The 351 is a bit taller and therefore the intake manifold is wider.

 

289/302.5.0's have an intake that is right about 9 inches wide, valve cover edge to valve cover edge. A 351W is about 11 inches wide. The two inches difference is easy to spot after you've looked at a couple examples of each.