I have read about, and experienced, the problems fitting no 4 barrels to high walls. I just tried to screw an octagon no 2 weight barrel onto lo wall actions. It goes on one but the flange around the forearm socket on the front of 2 of the  actions hits the corners of the barrel. I had the same thing happen with the high wall barrel - fit fine on some and not others. Is this typical?

The two low walls that bind the barrel on the front flange have grooves milled into the top of the receiver rings. The one low wall that the barrel screws into does not have a groove in the top of receiver ring.

I measured the space between the round top flange (1.10") and one with a groove in the top of the receiver (1.075") but I don't know if that has anything to do with the receiver tops.  The round top was factory fitted with a #2 barrel. You can see that the factory has beveled the flange walls thinner near the top of the receiver.
Stractor, you can file a taper on on the flange if you're careful and not mar the face of the receiver.  I had to do it on a highwall action when I had it fitted with a #4 barrel.  I used a diamond stone to cut through the case hardening.  Slow but it worked well.  Bob