Hi. I once replaced a 302 in a 73 Mustang FB with a 351W but had trouble because the spacer plate between the bellhousing & the engine were not the same as well as the flywheel or ring-gear being different sizes. The starter location holes run through the plate and these holes on the 351W plate did not line up with the starter holes on the C4 bellhousing, and the ring-gear was clearly too large. I had to either use the 302 plate and
ringear or use a C6 or FMX trans. I don't recall which I ended up doing. So pay atention to these items if you make a swap.