I found some info on the VST nozzles in California:
https://ww3.arb.ca.gov/regact/2018/gdfnozzles2018/isor.pdf
If I'm reading the diagram and chart correctly, there is about 2.6" of insertable length until the aspirator port. Meaning, I need gas to start flowing downward before 2.6" so I don't get flow back. I also am not sure those VST pumps are going to like my vented tank (a spring loaded valve on the vent line may solve that problem if it doesn't work).
The "nozzle latch ring" on the VST nozzles should retain the nozzle to my gas neck. However in my earlier tests I still need to solve that problem for other pumps. It seems that the fool proof solution to retaining all gas station nozzles so they don't slip out is to use an "unleaded flapper" (basically a smaller hole within the gas cap to "pinch and grab" onto the nozzle, just like the stock TJ). The insert could be removable so if I find that I'm using dump cans often I could increase the hole size again, but honestly 9 times out of 10 I'll be using a gas station pump so I want that to work best.
I received the 45* and 90* rubber angles and am playing around with ideas and then will start testing them at gas stations before cutting the top.
Does anyone have a junk soft top panel with tinted windows I could use for practice cutting and make sure it cuts how I think it will? TJ, LJ, or ripped is fine. I'll happily pay shipping.