I can see one problem with using the Marbles sight. The aperture intrudes into the space for stripper clip usage. The few times I carried a M1920 hunting I carried spare cartridges in M1903 Springfield clips. (They feed cartridges into the magazine slicker than goose grease.)
Hopefully with the addition of the peep sight you would not need all those extra shots....
When I looked at the fit of a Miller-Kodiak mount on a 1920 the bolt clearance became quite apparent - to mount a scope without modifying the bolt it would have to be quite high and I don't think any of the Stith's would be high enough. I have some of the Stith rears for the Winchester 70's and they are not very high.
Here is some information on Weaver N mounts, including the 1920 which has a note about bolt modification for the short mount -
- Savage 3, 4, 5, 6, 7, 19, 23, 33, 219, 40, & 45; low = N2, high = N3
- Savage 20*; low = N1, high = N4 - the * indicates the bolt handle must be modified for low mounting
- Savage 25, 29; low = N5, high = N5
My thoughts for the 1920's would be a Miller-Kodiak type mount with a long eye relief scope like those used on top eject Winchesters - this would not require adding holes and should put the scope far enough forward to use still use stripper clips (for those who require extra shot fast).
Here is the picture of the Miller-Kodiak held on a 1920/26 (could not actually mount it because there is no dovetail for a rear sight to use) -