trying jacking up the rear of your truck and grabbing the tire on the top and bottom and try to move it in and out. on mine i can move my tire in and out quite a bit(not sure about measurements). it could be b/c my bearings are a bit worn, but i doubt it.

i also doubt that you are going to be able to effectively do a rear disc swap for less than $500. from the price of the brackets, calipers, rotors, adj. rear proportioning valve, and larger master cylinder to compensate for the increased pedal travel. its going to be expensive.

and honestly, if your wife or girlfriend is anything like mine, you probably care about the "brake" problem w/ her truck a lot more than she does and she won't care, or know if she has disc or drum brakes. let alone a turbo charger. but everyone is different haha.