rivet hole location?
get a cheap set of transfer punches from your local harbor freight store...about $10.
clamp the receiver scecurely to a flat surface.
block the trunnion up to the same height it will set in the receiver. the height can be established by sliding the trunnion partially into the receiver and trialing a block of scrap steel or wood under it.
slide it back along the ouside of the receiver to the front to rear location you desire.
slip the correct size transfer punch thru the trunnion rivet holes and give it a light tap with a hammer...just enough to leave a visible mark on the receiver.
swith the trunnion to the other side of the receiver, making certain to position if front to rear in the same alignment as the first side.
repeat the transfer pin marking process.
double-check hole locations match side v. side by measuring with a 6" machinist scale with .010" graduations...$3 at harbor freight.
deepen your transfer punch marks with a center punch...$1-2 at harbor freight.
drill on size with a drill bit sized by uzing the trunnion holes as a gage. note: not all trunnion holes are the same size in some cases.