Thanks for the suggestions,
I got an answer from the Brownell's guntech guys. They said I have to make my own offset screwdriver (which is what I had already done) because no one makes a driver small enough to fit into the receiver and remove the screws.
I'm sure I am not the only one who has had to remove these screws so I still wonder what other people are doing.
Scorch- I may be able to fit a mini-driver inside one of the screw holes to reach the screw on the opposite side but that only works for one screw. I still need to use the offset driver to tighten the other.
best wishes- oldandslow