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