You are correct in thinking that the limitation is the barrel metal around the chamber. Hi-walls are hell for strong; even deliberate attempts to blow them up with all kinds of .30-06 blue pills and blocked barrels failed back in the day when they were using them for ammo experiments a lot.
I think the worst that would happen is that you might jam the threads of your barrel into the reciever threads so that ever removing it would be very difficult, and or/bulge the chamber a bit. Neither is a good thing.
A modern rebarrel would help since it would almost certainly be tougher material than all but the last VERY few originals Winchester made in 7x57, .30-06, etc.
In you need a real cannon, why not swap for a large-thread action or get one from C. Sharps? If you don't need a cannon, try a .25-35 and handload to get the most out of it.
The only small thread Hi-wall I've got is a .38-40--not exactly a cannon....
