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.

I'm typically .070-.090 on the tree, sometimes I squeeze a .050 out. I think twice I've been better than a .050 but that was pretty much guessing or pure luck. When I run with only the 2bbl I run with the secondary wired shut that way they don't happen to open their selves inconsistently.

It sounds like when you say you are running a 2 bbl that you are actually running the front half of your 850 4 bbl, if that is the case then perhaps a much smaller 4 bbl like maybe a 600 or 650 would give you what you are looking for. Probably have better throttle response and power than half of an 850.

I have been slowing my car down from 10.80s to 11.50 for about 12 years now, I run 11.50 Index on a .500 pro tree. I use a Moroso throttle stop ( bolts to the drivers side rear carb stud ) and I just adjust it in or out to go slower or faster in my application my secondaries are barely opening . I have tried the E.T. Genie as well as the Willys adjustable throttle stop ( plate moves in and out ) but I found with them they killed to much MPH so I went back to the bolt set up . This has worked very well for me .. winning two track championships with the set up as well as going many rounds and a few number one qualifiers ( dead on 11.50 in qualifying ) . With my current motors ( only a few months old ) power band I have found a glitch in my set up.. in good air I adjust and get to around 11.45-46 and another slight turn on the bolt puts me at 11.60s so I recently added another Willys setup even though it kills mph I am hoping with my more hp and tq. motor and only needing a slight adjustment for 11.50s it won't kill to much mph. I tried shallow staging on a .500 pro tree and was struggling much like you I got some advice from two very well known and successful bracket racers : Deep stage and stay with it until you get better... I have and it really helped my pro tree program ! and I foot brake and can hold my own against cars with two steps and trans brakes .. my lights and 60 fts are just as good as most of my competitors . Having a car that 60 fts well is also important ..my car is between ..1.58 - 1.62 deep ( 1.48 -1.52 shallow ) on the throttle stop. I also recently added a DD starting line controller its a lever that attaches to the side of the shifter and the bottom of the carb linkage .. its adjustable and spring loaded .. you adjust the lever travel and set it at your desired leave rpm .. makes it easier to stage I set mine at 2,000 rpm .. you don't have to look at the tach making staging easier .. push up on the lever to stage once you leave the line just let go of the lever