Block codes on a 400 specifying manual or automatic transmission only relate to what the engine originally went to correct? No difference in the block?
Same for heads? What I'm asking is can a manual stamped block and heads bolt up to an automatic transmission. Maybe a dumb question, With all the knowledgeable people on here someone could educate me, just curious. Thanks for the replays.

Yes you can bolt the tranny to that block. Some components are configuration different when they are automatics vrs standards. For example, carburetors and camshafts are generally configured slightly differently.

Generally, GM rarely builds siminar parts differently. I put a 89 Camaro 4sp BW T10 in a 68 Firebird (was a auto 2sp). Most everything bolted right up and the holes for the linkage were already waiting for me on the frame. My engine block was a 70 GM ?? and that went into my coupe as well. Next thing I wanna try is putting in a GM electric motor...see if the bolts match up? lol

Have seen that too. Seems like blocks were cast the same and received their trans designations after the fact. Notice auto blocks will have bell crank pivot ball hole drilled and tapped. Auto cranks are also machined to accept a pilot bushing/bearing.