> The 351M is a long block.
A long block is an engine (normally rebuilt) which has had the pistons, 
crank, rods, bearings, cam, freeze plugs, etc. (short block) and also the 
heads rebuilt. A long block can be bought for most any engine there is.
A 351M is a 351 C(leveland) which underwent a factory revision to become the 
351M(odified).
A 351W(indsor) is your basic small block ford. The W's and M's had a taller 
deck height, and heads (at that time) which flowed better. I think they also 
took the 351M up to a 400M for a couple years, but I do not feel like looking 
this up now.
            Gerry
---
---------------