Nalajr, your idea's are good. I added an extended mag tube to my stock M1Super90 Tactical and changed the pistol grip stock for a straight stock. I added a barrel support/clamp, and that is it. The side saddle is held on with the trigger group pins being replaced with machine screws, so I don't think you need to worry about drilling for a side saddle. I have used mine for 6+ years in 3 gun matches, and it performs very well the way it is. The biggest issue with a Benelli is putting too much weight on the gun and causing the recoil system to not function reliably. Add parts one at a time and test it, and add more. When you get it the way you want it run it hard. Don't baby that baby!
Oh yea, I use 2 point slings on everything I sling. Makes transition to the sidearm easy and helps secure the shotgun.
M1Super90 Tactical with the H&K M1Super90