There are differences in some internal parts between a 289/302 and a 351W small block Ford that make it easy to tell the difference when it's torn apart and laid out on the workbench. Sometimes though we just want to spot one in a row at the wrecking yard or in a car at a car show. The easiest way I've found over the years to spot the difference is simply to look at the left (drivers side) front of the block just above the front cover where the water pump mounts. The block has a 1 inch taller deck on a 351W engine, and it stands out quite clearly when you know where to look. Notice that there is very little space in this area on the 289 in this picture, then look at the 351W........there's that extra inch!