Change rear shift coupler on vw microbus

my 1966 microbus broke its rear shift coupler in half. i have the new part, but i can not remove the screws that hold the part on the shaft. the screws have no head for a wrench or a slit for a screwdriver. what can i do?

You’ll want to post this on a VW forum that specializes in the old Microbus, like those at thesamba and vwvortex.