An update:

I welded the bottom plug into the tank Friday when I got home. Actually
I am quite pleased with the results. The penetration wasn't quite as
good as I would have liked to see (Man, that's some thick stuff!) but,
1200psi should be no sweat.

Saturday: made a trip to the hardware store.... I bought steel fittings
for the tank to the regulator, regulator to the hose.... I don't have a
needle valve yet..... This should be sufficient for now........... Oh,
and I bought a manual operated valve to blow off tank pressure. The
blow-off valve will be seperate from the regulator........ I bought a
big pipe cap.

I didn't have a drill and tap big enough for the pipe tap at home so
it'll have to wait untill I can di it at work. The cap is about 1 1/2 -
18 thread...... This is big but still much smaller than a chunk of dry
ice..... Guess I'll have to break it up into pieces eh?

Also, the hardware store did not have a pressure gauge that would read
2000psi...... Hopefully I can stop by the welder's supply on the way
home. Right now all I have is a 0-200psi low quality gauge and a nice
little gauge for my regulator (0-160psi I think).