The supporters have a threaded screw that attaches them to the barrel. The screw was then brazed or forge welded in place and the heads ground flush with the sides of the supporters. Depending on how deep the slot on the screw head was you can still see it on some examples.
I believe reproductions from The Rifle Shoppe are made with a round barrel that is threaded into the square portion of the barrel, which is cast with the supporters attached.
If you are intent on restoring your Hall you could probably get a new barrel from TRS and have a good gunsmith install it. But in all honesty it is probably not worth the expenditure. I'd be interested in seeing what your gun looks like though.