Quote: Another picture which might show the gap better.
the gap is for socket clearance.
on a magnum head,they have tubes to press down in those pockets and use a 5/8" hex plug. remove them to use a LA plug for a wider heat range on magnums.
I go the other direction and only run the 5/8 hex plug in everything. To the op, the pic kinda looks like the seat area is tapered? I'm thinking its an illusion and the seating area is flat? correct? It should be. Autolite 3923 should work fine for most mild street engines.
