From the Alliant manual. Federal paper target,Federal primer, Wads;Fed 12SO,Win WAA12F1,or Rem PT12. Use either Bullseye or Red Dot @ 17.5grs all give less than 6000psi with 7/8oz. Some of these loads require a 20 ga card wad in the shot cup.
Here is another. Federal gold medel,Federal primer,Win WAA12F1.Bullseye 17grs,or Red Dot 18grs with 7/8oz shot. These require 1 or 2 20ga card wads in the shot cup. Less than 6000psi
From IMR Hi-Skor 800X loads; Winchester AA hull(old), Win 209, 21.5grs 800X,WAA12 wad with 1 20ga card, 1oz shot gives 1130fps and 5600lup pressure.
Some of these wads are no longer available. The Remington PT12 may have a diffrent number. The 1oz AA load seems like a good hunting load for your old gun.