Easy to tell. MII frame mounts use horizontal bolt to secure engine mount to frame mount. Late Mustang uses verticle bolt at 45* angle to secure engine mount to frame mount. Late engine mount bolt is metric 14mm.
Late 351W mount should secure engine 7/8" below where MII mount did. Early CR SBF frame mounts were the same for 302 and 351W. CR never envisioned the popularity of the 351W motor. The 351W sits too high to accomodate more popular intake/carb combinations like Ede Perf RPM. What CR advised was use of shorter Performer instead.
The 351W also has clearance problems using LF1 full length Ford
oil filters. Filter hits drivers side frame rail. Fix is to use shorter LF43 filter. This is the standard small block Mopar (318/340/360) filter.