[MusicMan70]

There is a casting number on the rear driver-side of the block just below the head. Yours may have a draft tube but the photo shows the canister. I have seen a number by one of the freeze plugs too.

The intake is dated as well; I've seen by the 1&3 cylinder area and 4&6. Also the exhaust manifold has a date. My 401 was reportedly a replacement engine so I have different dates; 74 & 79.