Those are 427 marine heads. It could be the 300hp 427 marine. The 12 DIF you see really means nothing important. DIF is the foundry it was cast at..Dearborn Iron Foundry. The 66-427 may or may not mean it's a 427 as I said above. If it is a marine 427 it will have brass screw in freeze plugs. Watch if the block has been run in salt water most of it's life. These ran in both open and close loop systems so it could be either if it's a marine engine. Another thing to watch is the rotation of the crank as marine engines also used reverse rotation in twin screw yachts. The
oil slinger grooves on the rear of the crank are machined in the opposite direction. This can cause a rear main seal leak when used in standard rotation applications. I'd ask for good pics of the engine. You'd want to see the crossbolt mains if it was a 427 or ask him anyway??
G.