I have an 1978 351M motor that I have completly stripped down to the block. Getting it ready for a rebuild. The motor came out of a truck in the scrapyard. The scrapyard said it was a 400, but the emissions tag on the valve cover says its a 351m. Is there any markings on the crank that can help identify what I actually have? Or the pistons?
I hate to round up a 400 crank if I have already got one.
Thanks in advance. Jaret

 

There should be casting nunbers on the first counterweight on the crank. A 400 crank will be 5M, 5MA or 5MAB casting. A 351M crank will be a 1K casting.