I'm pretty sure you don't need the gas tube, but others have had success with drilling out the hole and using a SS tube. The seal is actually made on the SS face around the gas tube, not the gas tube itself. Even if the tube is cracked, it should still work. I just put a little keg lube on it, and it keeps it to where I can push it in and out without too much trouble (no worries with cracking).
I was able to make the Williams gaskets fit. Yeah, they're probably taller than they should be, but they're nylon so they do give. I got the threading started and then took my 7/8" box wrench and started cranking down on them. They tighten pretty "easily" (read: not easy, but not impossible) and then they get tough to move after a certain point. That's where I stopped. I've got pressure on one now, and I'll update if it's still holding pressure in a week.
I guess I can be part of the experiment to see if the Williams "gaskets" work long term.