I've never tried interchanging a 301/400 starter because just looking at them side by side there is a big difference in heft. I guess if it actually bolts up and mates to the flywheel properly it should work, but it is asking a lot to crank a high compression 400. I do know that when I was running the HO exhaust manifolds on a 400, they were so close to the starter, heat soak was a big problem. The 301 might not suffer that way, being so much slimmer.
