I haven't opened up either of the two phones you've mentioned, but I can tell you this, that it's highly unlikely to work. The thing is, each logic board is custom designed for the phone it's in and the available space inside heavily determines the shape and size of the board and the placement of the connectors.
So far there have been no iPhones that have had compatible logic boards, and I see no reason to believe the 14 Pro series is any different. Not one single previous version of a Max or Plus model's board has been interchangeable with it's normal size sibling so it's unlikely the 14 will be either.
As I said, this is far from authoritative since I haven't held either board in hand, but based on Apple's history I feel confident stating that they won't interchange. I could be wrong and I'd be really interested to hear if I am, but I'm betting they won't fit.