A Model A frame is a flat frame in that there is no rear kickup on the side rails. A 32 for frame has a kickup at the back. Corresponding, the Model A body underside is flat while the 32 body has a raised portion at the back to clear the kickup. Also, the Model A body is narrower than a 32, so you have to either widen the body (ugh!) or narrow the frame and cut out the rear floor for the kickup

If you havent bought your Deuce frame yet, people like Hot Rods and Custom Stuff (Escondido, CA) sell a Deuce frame made for a Model A body....right width and a flat rear portion.