I talked to Frank and he told me that old style glass tube is:
"Originally it would have been a 1/8 OD tube, fitted between the tops of the ports, a common fix is to drill out the port so a longer tube will fit into port same as later models. Seals cut from silicone tubing should work for either."
I think I'll be going the "drill out the port" route, so a longer tube can be installed.. It will be tricky with this soft metal fitting and I might actually talk myself out of doing it. But I am all out of small glass tubing. If it isn't one thing, its another - I knew I should have bought a larger amount of tubes a year ago!