A big question for me is how will this type of heavy duty regulator perform in the presence of feedback pulse from the engine's inlet? we know standard (cheap as chips) ones tend to shut down under pulsation and do not have enough gas flow any way, I note you have a very nice braided hose too that will probably help those pressure pulses to get to the regulators diaphragm
Do you think you can come up with an easy way to measure flow as well as pressure? if so it would tell us what was going on between a static and dynamic test and if the regulator was affected at all.
Very nice build and up to your usual standard, good luck