I'd he's not afraid of tax stamps, I'd start w this upper:
BCM LW fluted 11.5-in. Take off the dust cover, remove & plug the forward assist, drop an Aimpoint H1 on it Zeroed for 100 yards at the top of the dot & don't even bother w BUIS. Oughta be good to 200 yards easy.
Put it on a good polymer lower, w a decent trigger, and a standard RE sans stock and call it a pistol until the stamp comes in. Get 20-rd Magpuls stuffed w 40-gr pills. More tissue damage for gutshots; let those bastiches suffer...
Oughta be Uber Wulf Defense Systema, and feathery enough for a mature shooter who packs a Whelen regularly.
I'm about to turn 55 and am doing sumpin similar based on an LMT Mk18 upper I Grabbed after Newtown Panic began. I'm replacing the A2 FH w a Troy Claymore to push the noise away from my raggedy azz remaining hearing.