As far as I understand it, the mag box is the same, but the stock inletting is different.
I have 2 rifles that were originally the 2 piece, I swapped them out for the one piece, the inletting needed minor alteration for them to fit.
Maybe someone knows more precise info that will be more helpful, I've never gone the other way.
May I ask why you would want to ditch the one piece bottom metal?
It's stiffer than the 2 piece.
Cheers.