Hi, Mike! First the roof from hell, now this. Welcome to the world of T1N Interstate ownership.
The good news
: Your tank appears original or near-original, but in unusually good shape for its age (while you are under there, you might want to take a pic of the welded-on spec plate, to have for future reference). Mine was shot, and I had to replace it
The not-so-good news
: Your flex lines appear to be original
and do need to be replaced. See this description here
for how to go about that.
The news that is neither good nor bad, just different
: I have seen many an older Interstate in my time, but I've never seen that configuration on the tank. I've only seen the typical fill bleeder, to bleed head pressure during filling. Therefore, I can't really comment on why the heck that was done to your tank.
Anybody else have ideas?