10-1/2# would be fine for a 470 as it'd essentially be a 458 of that weight. the 500 jeffery i built only goes 11 after adding 10oz of lead to the butt and it's not unmanageable at all.

in this case i'd be more concerned about the stock than i would my shoulder. i think it was flaigs back when the red label came out that did up a 375 o/u for john amber on that action and if i remember right (think is in the '78 gun digest) the conversion ran about $4k back then. but a 375 is a different kettle of fish from a 458 class round. and an o/u DR just would not be the same as a sxs.

you'd never get another DR that cheap but personally i'd shy away from this one. it may be perfectly fine but it looks like some kluged up affair. i'm sure the bss receiver is really strong but i'd have some concerns about it too. it just doesn't look like a good idea.

roger