Actually there were 3 351 blocks. The 351 Windsor, the 351 Cleveland (1970-73) and the 351 M. The 351M is the same block as the 400. The Windsor and the early cleveland used the mounts that were the same as the 302 and a bellhousing that was the same as the 302. The 351M and the 400 use the big block bellhousing and they have the same mounts as each other. If you really want to get confused, the FE series (352-427) had totally different mounts and bellhousings than any other series. Makes engine swapping a lot more difficult than on Cheebies.