Depends on the cover you buy. Chances are, for the '75, the cover will hold the rear lights directly to the cover, so no supports will be needed. 

Cindy, I installed a FG rear bumper for a friend several years ago and you are correct, the tail light mounts and center reinforcement are not required. The new FG rear bumpers are sustaintial enough to hold the lights and the Corvette letters in place. The reinforcements were needed for the original urethane bumpers that were somewhat flexible. I recommend a few trial fits of the bumper to make sure everything on the backside clears. You may need to do some sanding and fitting if you want it to be perfectly flush to the body. The only problem I had was the license plate light, a little cutting and fitting was necessary to get it in there and clear the main bumper beam. Good luck, I hope this helps !!

Cindy, My 75's, both/neither of them have a honeycomb support. Tail light supports, and the center support are all mine have. Not sure if the corner supports for the bumperettes can be removed for application or not. Depends on your choice of bumper. I have seen a couple refits with NOTHING under the bumper but the frame, as a Good fiberglass unit does not require any support except around the body.