What's typical of your .500 Pro Tree RT? I don't have much experience foot-braking from a Pro Tree, which is why I ask.

You can likely jimmy the secondary linkage so that they don't open or only open slightly. Probably need a long link that you can bend to work... or maybe something even cruder like remove the link and zip-tie the secondaries shut?

FWIW, I've been considering trying local 7.50 1/8 and 11.50 1/4 index classes this year in my 1320, although the car is pretty far off the mark, especially in the 1/4. Might have to look into easy weight removal tricks to squeeze what I can out of it.

If I can get the old car dialed in on the track, I expect it would be a better fit in the 6.50 / 10.0 classes than the 1320 will be in the 7.50 / 11.50.