hello Bryce,
first off these trucks after then get some hours on them do not start very quickly anyway, they always turn over a few rounds before the fire off, has to get the lp gas up to the mixer and that has to pump enough vapor into the engine before it starts up.
The pressure regulator (vaporizer) is a model J in the older trucks but they moved on to another Cobra version of that regulator later on. The biggest difference is the primer button is missing on the new ones and the relief spring inside for the inlet port button assy is a blue spring i think, different pressure regulation. I have interchanged them and have had no issues. Your 2 biggest problems with these regulators are either contamination from oil buildup or antifreeze leaking into them causing the diaphragms to go bad. Generally they will start freezing up after a bit or they just will not put out any vapor or it will be restricted.
Another issue is these trucks have this fuel control solenoid valve (FCSV) mounted in the same area as the regulator and filter assy, when it is operating correctly you will hear it rattling, if you do not hear that it is probably stopped up or bad, it does have vac hoses that hook from it to the intake/mixer vac hoses. This will be shown in the diagrams i have.

send me an email at my address in my signature and i'll send them to you.