Brian,
Yep, those are the ones! I was able to salvage one out of the bumper core I bought, but the other broke, even with several attempts with a rosebud tip to get it out. I never knew these were there until I bought this core with the brackets attached.
Pat, I don't have a picture handy. Brian's description is better than mine on the location. If you have any of those screws, I'll take em!
Joe, these screws go in from behind the bumper. It's a little 3/8 hex self tapper that locates the flat plate where the PL housings attach. If the bumper you removed from your 65 still has all the brackets on it, you'll see them from the backside.
Mark