Very similar to my Mercury camshaft thrust plate screws. I had to dig around the shop for a bit that would get them out. Surprisingly I had one in a case that came with random oddball bits.
If you own an old Chevy half-ton, '37 to '55, or more, first thing you buy is screwdriver set with clutch ends....
I saw this one time on the out house door at the county farm . Anti Theft , so no one could remove the hinges and join you till the show was over .
They are Clutch head screws that were used on Chevys for a lot of years. You can get sets of bits or screw drivers on Ebay, in some tool stores or maybe the simplest is on Amazon.
I just grab the worst flatblade that fits in there, and have at it. Then toss the screws and replace them with socket heads.