It's a 351 M. "M", NOT MODIFIED like many peopele call it. The M means the motor was made in Michigan. The 400 is just that a 400. BOTH ARE TURDS!! I had a good sounding 400 but the ports and intake runners are just too small to get good power out of 'em.
The best thing about a 351M or 400 is you can throw them in the river and put a 429 or 460 in it's place. :wink:
A long time ago I was a Frrrrrd guy. I do still like the late 70's 4 wheel drives.