I think we are talking about three different engines. This engine I believe is a Chevrolet engine (194/230/250/292) due to the forward location of the distributor and spin on oil filter. The pics Mark posted above are the GMC 228/256/248/270/302 that the Wayne/fisher 12 port heads were actually made for. The engine that comes in the AMT ‘51 Chevy kit is a 216/235/261 “stovebolt” six (which was the basis for the blue flame ‘53 Corvette engine). AMT supplied the Fisher head and 12 terminal distributor to emulate the larger GMC six even though the 1-1 parts would not fit that engine. That is my take on it.🙂
Edit: The stovebolt and the GMC both have the distributor roughly centered on the block and are fairly similar in appearance.