Would be a significant weight reduction figuring first the USAF removes: guns, turrets, ammo feeds, gun sights, tail gun radar, main radar & computer (heavy vacuum tube monster as I recall is around 5000lbs), optical bomb sight/system, bomb racks, and whatever else enables it to be a "bomber".
Purchaser can remove stuff like: cooling system for that vacuum tube monster, many wire bundles that went to mission equipment, the big generators that produced power for mission equipment (replace with smaller/lighter), accomodations for a full crew, replace gunner blisters with flat (less drag) viewing windows, replace radome on bottom with flat pannel, as obvious items and must be more......
Considering B-36 is designed to carry all the above + fuel + up to 86,000lbs bombs + 20mm ammo --- at this point it is hotter than any USAF B-36 ever flown.