Hi Jeff,
It looks like your mountaineering pack has a modified U-shaped aluminum tubular stay where the bottom of the U shape sits in a large pocket on the back of the current hip belt. Short of sewing a pocket onto a new hip belt (and maybe still not being satisfied with the load transfer), an alternative option could be to find all metal, heavy duty tubing clamps like these

in the diameter of the backpack stay, and then bolt on a Seek Outside or McHale style belt with grommets (I’ve seen used Seek Outside belts a number of times for about $40 on Gear Swap and the Seek Outside Adventures page; I bought my SO belt used to attach to a MYOG pack). Or for a cheaper option, if you have an old external frame pack of any brand or can find one at a thrift store, their hipbelts usually have grommets where the cotter pins attached, but you could bolt them on to the frame just the same. Just an idea I had that I hope makes sense. Good luck!