The receiver "ring" portion of a Thompson receiver is flat sided. I suspect that something like my flat receiver wrench would work. I've used it on 94 Winchesters, Ruger No.1s, etc. It is just two 1" square bars of steel, clamped together with Allen head bolts. One bar is turned to allow a piece of pipe to be added as a cheater.
If a barrel is truly scrap, a pipe wrench may well be appropriate. I've done it; I've also turned off barrel shoulders. If the TM suggests a strap wrench, they obviously did not consider the barrels to be torqued in too tight. If a strap wrench would work, the rope trick might be worth trying. If I were doing one, I would just machine aluminum bushes to fit my barrel vise and the specific barrel.