If your Model A is 1930-31 it is not too bad. Remember the radiator neck will be in the wrong location and have to be moved. The hinge bracket will have to be changed, the Model A used a rod and the Model B was a formed stainless piece. I believe the light bar will need to be bent to clear the shell. This would be a good question for HAMB.
Moving the radiator neck is one problem. The shape of the top tank may need some massaging. The lower pan will need to be changed to the aftermarket one designed for this setup. and the light bar will need to be bent to go around the shell. I found it easier to buy the 32 radiator and not modify my original 31. Also you will have to add the Model A hood clip to the 32 shell. Using a 32 radiator it was not a big operation for me. I added the 32 headlights to match the shell and it looked good.
Depending on what you are doing overall you might relocate the water neck inside of the engine compartment and pressurize it (4 LBS if using a stock radiator). Attach a '32 radiator cap using a strap under the cap (or just fill the shell). These pictures are from my '32 but same idea.