u/Hot-Half-1783

First time doing any level of gunsmithing work so forgive my ignorance.

Trying to mount a vortex viper red dot on my Mossberg 500 but I can't seem to figure out the top 2 screws (see pic). The back two came out super easy with a T10 torx but none of my smaller sizes (T6, T7, etc) seem to work on the other pair.

Does anyone know what type of screws these are? Am I going about this the wrong way?