Be aware that a 351W takes different perches and a different transmission, just like the 302. But I agree it makes no sense to do all the work and get less.

And a 460 can use the same tranny, in theory, as the bell housing bolt patterns are the same, but the 460's flywheel is 1/2" further to the rear than that of an M/400. So an M/400's manual tranny cannot be used on a 460 at all as the input shaft wouldn't let the bell housing reach the block. On the other hand, I don't know for sure about a C6 from one working on the other, but the parts catalog shows the case for the M/400 tranny to be the same as the 460's, as are the input shaft and torque converter. So, it should work.

 

I only suggested the 351 for the fact it's aftermarket support is huge if he wants to go to a Windsor series engine and stay a small block, he might as well get some kind of a gain. But yes, otherwise you are spot on.