Re: Savage Sporter 23B .25/20
These are good rifle buys if you want a 25-20 or 32-20 chambered rifle. Generally accurate with factory ammo. I have a 23B and love it.
As far as is known the stocks were not specifically numbered to the rifle as was done with the Savage 1899's and 99's. This is true for the Model 20 as well. The wood to metal fit wasn't as critical in the bolt guns presumably.
Your butt plate and stock sound correct from your description. you magazine description indicates an earlier design. Later 23B and C have a mag that is rectangular in cross-section without the cheese grater.
The scope mount may be a Mossberg.
The rifle uses the bolt handle and one other lug for locking. And it a rear lock design. You'll get headspace problems by trying to make the 25-20 more than it is. YMMV.