351 Modified in a fox?

The 351M is a big, heavy, worthless hunk of poop. I used to have one in a '76 Gran Torino (a car that I was STUPID, STUPID, STUPID!!! for selling for $1500), and that thing was a friggin' SLUG. I think they only had about 130 hp from the factory, tops. It was mostly a truck motor, a smaller version of the 400M motor (which also sucks, but not quite as much). It's strictly good for torque, and that's it. Some of the off-road guys like them for some reason, probably because they're good for climbing and never see any high-RPM runs at all, but in a Mustang ... forget it. They blow, trust me.

Gawd, I wish I'd kept that Gran Torino, repainted it, and dropped in a 460 (or at least a 351W)...

I've seen stories of people slapping on a set of heads and an intake to the 351M and getting atleast 350 Hp to the wheels. Still I don't think it would be worth the trouble to install it in to a stang. But it should be no harder that a 460 swap.