The only differance on the block is the spacing may be different where the motor mount plate bolts to the block. The earlier 5 bolt blocks had a narrower bolt spacing. The later 5 bolt blocks have the wider spacing that is the same as all later Ford small blocks. If you have the narrow spacing you will have to modify yours or find a set of wide 64 mounts.[img]/phpBB/images/smiles/icon_smile.gif[/img]