2 of the bolt holes in the late blocks is in pretty close to the same spot as the early 2 bolt blocks,but the frame perch in the mustang is not centered under those 2 holes like it is on the Galaxies,it is centered pretty much midway between the 2 sets of holes on the later blocks.When I've seen early blocks used in later cars they usually fabbed a plate that covered the 2 holes in the block with holes to allow bolts to go thru the mount,the plate and into the block and then had more holes for the mount to bolt to the plate,and then they had straps welded to the plate to pickup bolt holes elsewhere on the block.I don't know if this is necessary but the logic seems sound.