Have you considered
Lighter loads? I got my No.3 (.45-70) back in 83, and it was used. It also had a ventilated recoil pad attached over the steel buttplate. I guess the previous owner decided he needed it, as the rifle also came with 50 or his handloads, a 350gr RN at 2200fps!
I still have 9 of these rounds left. I save them for shooters who say the gun don't kick!
I an a little over 6' and an embarrasingly
little over 250lbs, and these loads walk me back about half a step when fired. Not for use prone!!
You might consider getting it magnaported. It won't reduce the recoil, but it will reduce the "jump" and might save your dental work. Or just get it restocked to something with a better profile.
Rebarreling is possible, but I don't think you can get one from Ruger. I did see a really nice No.3 at a gunshow a couple of years ago, restocked, and fitted with a long octagon barrel. Cal? .45-120!
I also have a No.3 in .22 Hornet. Sweet little gun, but so is the .45-70.
If you do get yours rebarreled, why not consider a wildcat on the .45-70 case? A 6.5mm on that case ought to give awesome performance, and you won't have to have any changes done to the extractor.