Have those two kits and was sizing up doing that fuselage-wing swap in both directions. I am building to have 1/72 models when done.
That said --- the B-29 engines are too large to be a realistic size radial, need engine/wing surgery to fix it --- B-36 wings being 1/72 are already good, would make changes to B-29 cockpit etc to bring fuselage into 1/72 scale, guns would scale up to 20mm.