First off, thank you all for sharing your expertise and kind feedback.

I've had a chance to cast the chambers and I've also received some S&B 9.3x72r loaded ammo. Rim size for the loaded ammo is perfect and the cast confirms a 72mm straight walled case. But the ammo doesn't fully seat, standing around of the barrel breaches by a small amount, roughly equal to the rim thickness. I will attach pics below showing this, along with measurements and where I think the cases might be hanging up.

Comparing measurements at the case head, the chamber is large enough for the S&B cases. But starting about 1/2" inch in, the chamber tolerance becomes very small. Starting 1.5" in, the chamber becomes straight walled to the case mouth. There is roughly 10mm of leade till the rifling starts, and that shows a 0.340" bore and lands at 0.358". No wear marks on the case towards the rim or the mouth...just in the mid section.

I didn't take a picture of it, the rifle very nearly closes on the loaded S&B rounds. I'm afraid to really snap the action closed to try to get these chambered but it's so close.

Unless there's a better idea, I will order brass and dies and try this with unloaded cases. If that doesn't work, then I guess it's either custom dies or have the chambers touched up with a the standard reamer. I'd prefer to avoid that if possible and let the next generation inherit this in the shape I found it.

Here are some pics:

Note below the left most measurement is the case head, not the rim, which as 0.492" on the cast.