Quote Originally Posted by vara4
351M Is considered a big block, 351W is a small Block. Big block 460,428,427, 390 should bolt in.
You might have to change motor mounts.The 400M will bolt right in, same block as the 351M just differant crank and rods inside. They are both related to the 351C. they use the same heads but the blocks are differant.
The crank and rods won't fit the 351C and the Intake won't fit the 351C from
the 351M or the 400M. I'd drop a 400M in, and find some closed chamberd heads from a old Cleveland motor. Slap those heads on and that motor will make gobbs and gobbs of horse power.

Kurt
Sorry, but if you had a 351 M in there, there is NO WAY a 390, 427,428 is going to bolt to that C6. (completely different bolt patterns). From what you have said, you could realistically do 3 things:

1.) Find another 351M / 400M and install it.

2.) Find a 351W C6 tranny (truck) and swap both the tranny and the motor.

3.) Do what I did and ditch the 351M, and the 351W, and install a 460. It will bolt up to your existing M trans. and factory parts are available to make this swap easy. The torque difference is INCREDIBLE.

Hope this helps you out, Snake.