Good to know that it's a -4AN, thanks for that bit of info. After some more reading I think I'm leaning towards the paintball co2 bottle now, those nitrogen bottles are only like 1.2cf of gas at 500psi. Won't last long even purging. Not really long enough to justify nearly $30 each, anyway. I think I'm going to go with this:
TRINITY PORTABLE CO2 SYSTEM FOR BAR KEG DRAFT BEER TAP KEGERATOR and add a hose with a 1/4 SAE on the end to plug directly on a service port. I can do a vacuum leak test then pressure test with propane, since I'm planning on propane for the refrigerant anyway.