Wanted to post my solution for the record...

Couldn't get the struct hole opened enough with a screwdriver. Ended putting back the bolt in the trunion, screwing it completely. Once 'closed', I used a drill press with a 1/2 inch drilling bit. This resulted in just taking out enough material. After taking out the bolt, I used the screwdriver method and opened the hole, inserted the struct and screw the bolt in. Perfect.
Tried with several structs, all fine.
Thanks for the suggestions.
Regards,
Edgar