here's the info, cut/pasted from here:
FE INFO

Another change to watch out for is the engine mount bolt holes on pre-1965 “FE” blocks. Blocks before 1965 had two-bolt engine mounts while those from 1965 and later had three-bolt engine mounts. This isn’t a problem if you plan on using a 1965 and later block in a pre-1965 vehicle.

Problems abound when using a pre-1965 block in a post-1965 vehicle because some machining and drilling are required.


this thread has a picture of the old-style mount:
332-428 Ford FE Engine Forum: FE engine mounts