Brian you just have to press them as flat as possible and work them in the slot. Here are a couple of truths, however: 1. The arc movement of your pedals is not a perfect circle and those pads will wallow out in a short time. The odd travel path ensures it. Even the pads supplied by GM up until around 1976...none of them last very long. 2. Make certain you adjust your pedals so that they travel (as much as possible) in a manner so that they don't strike the metal of the cab (up/down/or side to side). If your pedal bushings are worn out, this will be impossible, but we'll hope yours are in good nick. You can get an idea whether you have a problem by rocking your pedal side to side or up/down. Good luck. I finally made myself a hard plastic piece that sticks to the rod and moves around in the seal slot as the pedal goes in/out. This doesn't help with the noise, but it does stop the air flow.

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end