CONGRATS CHRIS! Any possibility we might see some video?
As far as the elevator servo mounting points at fuselage rear, I have always laminated a thin (1/16) plywood plate about twice the size of the servo trays to the inside of the fuselage to provide some thickness through which to mount the elevator servo trays. Otherwise, as you say, the fiberglass itself is not going to hold up and in some cases, could flex when subjected to high elevator pressures. With a Moki 250 up front, tail weight is not much of a concern for you!
I have never seen a Gee Bee R1/R2 that did NOT require substantial elevator up trim, so yours is no exception and a GRASS runway makes take-offs and landings a HECK of alot easier!
Regardless, in the hands of a bad pilot, the Gee Bee is a bad airplane, and in the hands of a good pilot, it is a GOOD airplane
