A 4.362 bore (.020 over if you can even get that size any more in a decent piston) and a 3.100 stroke will get you 371 inches as I assume the sanctioning body for Bonneville rounds UP displacement once you go .001 over you go up.
The above math says the displacement is 370.6072 so it would round up to 372 inches. Anything other than 3 zeros after the decimal point makes the round up.
All that being said, the 400 piston is so long it’s nuts. The decks on the block are far too tall for the stock 383 stroke let alone a 3.100 stroke.
If you have to go bigger than a .020 over bore you have to reduce the stroke even more.
Sounds like a bad combo to me.