Main Cap Question

They’ll physically interchange and, as indicated above, the 440 has a larger main bearing bore. The ability to swap caps from one 440 block to another depends on the accuracy of the main bearing bores between the two blocks. You can cut caps and align bore and/or hone depending on how much they differ, to bring them back to spec. I’ve also used 383 caps on 440s that were missing caps to salvage those but you need machining equipment capable of boring that much material out of the cap.