Just an update;
Went ahead and used dremel to cut small groove in screw then back out with flat head(with very little damage to chassis)
Per one of the cool and knowledgeable guys from lhs (superior hobbies), after I removed one screw I was able to spin the rear bulkhead itself instead of trying to spin screw. Sounds simple enough, but people including myself tend to over think things sometimes. Figured I would post this incase someone looks here in future with similar problems.