I had to change the mounts in a 77 F150 I had years ago when I went from a six to a 351-W,the 240/300 six has the same bellhousing bolt pattern as the small block V8s so you will only have to change the flywheel. The six flywheel will bolt on a smallblock V8 but there is a difference in balance as the small blocks have a external balance and the six is a internal I think.