Overbored

I've got a good looking, good running, booster leaking, 94 Silverado heavy duty K2500 with brake option code JB7. It's a 4x4, has 13 x 2 1/2 eight lug drums, 8600 GVW, 5.7. All the things that make it a JB7. ( Plus the sticker in the glove box.) I bought it in 2007. I ordered a booster from a local auto parts store using the JB7 code & discovered ( the hard way ) that the pushrod hole was too small to fit the brake pedal stud. Went to a different store that had some boosters in stock & found that option JB6 had a larger hole & would fit the pedal. With some misgivings, I bought & installed that one. It's defective. The outer case halves seperate slightly when the pedal is pressed so the master cylinder & brake lines move forward about 1/8th inch. The brakes work but it makes brake action really touchy & brake release slightly delayed. The truck's drivable, so before getting another booster, I'd sure appreciate hearing from anyone that's replaced this booster & if you had any problems with the job & with parts. Also, I'm looking for the best way to get the dang pushrod retainer clip off of the brakepedal stud. It took about three hours last time...