Somebody out there must have this part. I haven't owned an OHV Volvo for the past twenty years, but I remember this part vividly.
I also remember snapping one off at not too great a torque. I think stress gets them anyway. And I remember easily finding a bolt in my junk box with the same thread and length, and then grinding the head into a ball shape on a grinding wheel, quenching it frequently so the heat treat wouldn't be affected. I remember setting the valves, and the makeshift screw lasting a long time...but then, I've always been ridiculously lucky.