pulling to the right

He put the car up on the lift, and checked the dimensions of the wheel cylinders (which the shop had ordered) - they appear the same on the outside, but the insides were different diameters! One side is getting more drag that the other, which accounts for the pulling.

New cylinders have arrived, and Tuesday I drop the car off for the installation. But, here's the question:

After the car warms, I still get a screech on a hard stop. Could that be explained by the difference in drag? Or do I still have a (different) problem?
Did you mean one of the wheel cylinders has a different diameter inner piston? Sure that can make a difference! The larger diameter inner piston will exert more force than the wheel cylinder with the smaller piston. Once the cylinders are changed to be the same you should have equal braking (assuming the shoes are adjusted similarly). The screech is likely that one side locking the wheel up while the other one is still rolling, thus the pull you notice.