Not all bottles are covered by the testing excemption.
It has to have a specific stamp on it DOT-E7737-1800. This stamp only covers the bottle and not the bottle valve.
There is no legal need to test bottles that are stamped this way but I contacted a well known bottle testing company about 2 green 7oz bottles that came with my phantoms and they recommend not using a CO2 bottle more than 10 years old.
That's one thing we haven't got into, the lifespan of these bottles. There is talk within the testing fraternity about increasing the 15 year lifespan on certain bottles, and there are already 20 year bottles out there.
I'm working on 'If in doubt don't use it'. So my old colour matched bottles are now for display only.
H-Pac will test CO2 bottles but it costs more than buying a new bottle.
On a side note Wevo do 2 inch tanks with 3000psi air valves.
Can't help I'm afraid, I only have 2 3.5oz tanks. ones been side tapped to make an expansion chamber on a cocker and the other i use as the expansion tank for my double bottomlined phantom