Power Brake Booster Adapter Bracket

[70custom20]

I saw in another thread, someone had posted a whole sheet of GM PRO numbers for brake boosters. The JM3 reads booster, brake, 240mm high flow, while the JM5 reads booster, brake, 200mm high flow. I'm not sure what difference the milometer size has to do with anything. Also, would it be better to grab one of these boosters off of a early 2000's S-10 at the junk yard, or would it be better to buy one at a local parts store like NAPA, etc??