I bought a homemade tractor (you have to see it to believe it, I would be glad to email you pictures of the beast). I was told that it has a 351M, but I don't know for sure. I don't know what year it is or anything. Is there some casting marks or any other identifying features that will help me identify it? Thanks for you help.

 

You can measure the intake. The 351M has a much wider intake than the 351W.

 

email me pic or pics!
If its in the 335 family. its a 351c,351m, 400 of course. they have 8 bolt valve covers, rounder intake runners, thermostat housing is mounted to the block.

as for 351c and 351m/400, the 351c thermostat housing mounting is level with the block. The 351m and 400 are raised. I don't know off hand the specs but the 351m and 400 intake are wider.

As for determining between 351m and 400 you might have to measure stroke.

 

There should be a set of letters and numbers stamped on the underside of the block on, I believe the right front corner, right below where the head bolts on. Once you find those post them here and somebody can decode them easily.