This question is coming from a past 351m owner. My understanding was something like big block with small block c.i.d. is that even close. also if you wouldn't mind expanding my knowledge, give me the run downs on the windsor and clevelands. what are the differences and similarities. three 351's but a world of difference between them right? I am salivating like one of pavlovs dogs, anxious to learn something new.

 

Actually there are four Ford engines with a 3.5" stroke and 4" bore; the 351C, 351M, 351W, and 352.

The 351M was built off the same block that was designed for the 400. The 351M basically uses all the same parts that a 400 does except the pistons and crankshaft.

Ford uses engine families and not big block small block terms but yet some magazine writers that grew up with Chevy engines try to apply those terms to Fords.

You can find more info here:
High Performance Options for the 351M/400 Engine by Dave Resch