This is a photo of the Osprey S/Tgt. piston; counter bored as per my earlier post. The counter bore is 1/2" dia. X 0.200" deep; the angle at the point seems to be a std. 120 degree drill point. Hope this is of help.
ATVB
abellringer
https://www.dropbox.com/s/0nfy1qyjca...6.JPG?dl=0nger