Thanks Merv, Casey and B-29er. Good points b-29er. Looking over the Herc tail compared to the GP, I think I'll leave the GP tail as is, the fuselage body ending pre-elevator. Just widen the top and floor plates straight from base of cargo door to the tail box. Possible close the tail box or add an internal vertical support.
Building a Herc split elevator is not impossible, just a touch much for me right now. But I was looking at Herc rudders. Maybe extend the forward fuselage support almost to the wing trailing edge, running the rudder hinge straight up. This would give me a top rudder location for Position/Anti-Collision lights.
Empty CG will be comp'd by reinforcing or extending the Nose/Forward Fuselage. By the looks of the GP, cargo should sit between the leading edge and trailing edge of the main wing. This should be close enough to CG center to fly right. Most Herc drops I was involved in were done at a slow speed, quarter flaps, with a slight nose up angle. Everything (Everyone!) slid out fine, then Flaps Up/ Grab Air! LOL