You dont want an M, they look an awfull lot like Clevelands, but they arent. The heads will swap though.. They are a tall deck version with larger mains adn the 460 sized bellhousing pattern.

The Windsor looks like a wide 302, once you know what to look for, its easy to spot them and figure out what they are.

 

yeah the m is not a mustang motor ive seen them in the 71-73 cars, but u have to source a big block tranny etc the 351m/400 were victims of the smog era and some left the factory with 7:1[:'(] but with some new pistons,heads from afd a 400 can be quite the torque monster for a 4x4 it has a 4inch bore and a 4 inch stroke the longest of any ford small block

 

The 400 (if it is one) is actually quite a powerful motor if you build them right, and you can go about it surprisingly cheap...In stock form they made 400 ft lbs. That was made with 7:1 or so compression, 2 bbl carb and a whimpey cam. If thats not good, i dont know what is. These engines have the longest rods of any Ford engine, and the even 2bbl heads have quite large valves, over 2" intake. Alot of truck guys are doing a 434 stroker with flat tops, aluminum heads and intake with a 4bbl carb, a timing set and making 550 hp and huge torque for like $4000 dollars. Don't knock it 'til you try it.

 

theres a 400 build in hot rod this month i might have to build one for my truck

 

there is a guy with a 351c here in town (phx,az) and he wants to sell it