[Barry_R]

Ford used internal and external casting cores with darn near reckless abandon. The mirror image 105 only means it was cast at the MCC foundry. It does not designate heavy duty in any way. The 352 designation is usually - but not always - found on blocks cast at the Dearborn Iron Foundry (DIF). The center drain is common and does not mean much. The vertical ribs are most common on later service blocks - but again are not definitive. The 4.130 bore and a sonic check are your best friends here....