165 GR 45 Colt with 25grs of FFG with filler is a soft shooting load. Cut the 10ga down to 2 3/4" using 1oz shot over 65-75 grs of FFG and yer all set with your current gear.
20ga kicks harder than a 12 because of the light weight. If the Mighty 10 is too heavy, use a 12 ga. 60-65grs FFG under 1oz of shot.