68Z28Project is correct. AMK is probably one of the best resources we have for restoration hardware but it may not be identical to the original hardware originally installed. Here is a picture of AMK's screw #B-120049, 8-18 x 3/8 Zink plated that I purchased for this application. It is a plane head without the "C" marking RPOZ11 shows. It possible that there were multiple hardware suppliers for this application and variation can be expected.
RPOZ11, is this the original screw? What is the plant and build date of your car?
Does anyone else have an unrestored or original screw for this cowl induction relay application? If you do, please post a picture and note the plant and build date of your car.
Thanks!