the 351c, 351m, and the 400 were all in the "335" engine family. the 400 is the 351m with a 1/2" longer stroke. i think it's actually 402 or 403 cubes. it's good for trucks because that gets you more low-end torque but sacrifices horsepower on the top end.

my dad has one in his '78 3/4 ton. we put a new 280-300hp engine in it about 4 years ago, but even the stock motor had good torque. they sure love gas, though, and he has to run premium it it to keep it from knocking. i wouldn't recommend that motor if you had other options.