Re: 351 Clarification
 

As Lewis Matkin stated, look for the oil line to the carburetor governor. A 351 Magnum would have the governor, a 351E would not. Spin-on oil filter adapter makes it more likely to be a 351E, but not a sure way to tell.

Re: 351 Clarification
 

So far it seems....from members:

1. I have I-Beam exhaust.
2. Jolly says 351E is essentially a Magnum.
3. 351E has no governor.
4. In 1966 the 351E was offered series 1000-3500 trucks.
5. Spin on introduced in 66-67, I have that and that indicates 351E/351M.
6. Magnum has trapezoid carb pattern. I have that.
7. The block is just marked 351.
8. Magnum head cast no. 2421158
If I ever tear it apart, I will check size of exhaust ports and check head casting no. It could be a dressed up non mag.

Thanks to everyone for all the input.