Oldgreen51,
I kind of like the clutch head screws and bolts, after completely disassembling and reassembling an entire truck ('50 COE). I much prefer them over slotted or phillips heads. To work with these fasteners you need the proper drivers or bits and before you attempt to mess with an old clutch head fastener, you need to clean out the hole. The sides of the hour-glass shaped hole are straight, so to get the driver in there all the way, you need to clean it out with a sharp awl or other tool. Get all that rust, grease and dirt out first. If done properly, you will either remove the fastener or snap the head off the fastener, before it slips out. What more could you ask?
If originality is not important then use whatever is handy. I would go with a torx, square hole or other straight sided fastener before I would use a slotted head screw or bolt. I was trying to retain an original appearance to my truck so I bead blasted and reused all the fasteners that were not damaged upon removal.
It takes many years of carefully removing the original clutch head hardware to come up with enough extras to get you through an original restoration.
http://img.claspics.com/w8cp5hb/hhuvt3pj/1371063541-830.JPG_m.jpg?1371063546
