tires and brakes on my four winds chevy 3500 chassis

Quick check on O'Reilly's website indicates they are disc brakes in the rear. You should be able to look through the wheels to verify.
Make sure you replace the pads with ceramic severe duty.
Shimmy would come from the front wheels. Expensive to replace rotors. May not have enough to mill.
Make sure you change the brake fluid.
Have someone check to see if there is a proportioning valve for the brakes. Early GM cut away chassis had an adjustable proportioning valve.