Chuck nail polish is a key "tool", did use it here as well, ok the color variety in my houshold is humangous..
No, I used the nail polis on the tip of the rod to finalize minimal gap, as measuring the gap is hard to do as no real ref. point. Several attempts in/out until binding then 1/4 to 1/2 half turn back of the booster push rod.
KEY is a good seal as well, the seal between the bake booster and the push rod (in my case the push rod part of the main). I had sever issue here as I lost vacuum, resulting in missfire of the engine in push mode. I added 2 rubber seals from the plumbing industry/forcet stuff, as there was a decent gap on the main side to accomodate this set up. Top result!
Matthias