I have installed factory bumper guards on a few '64-'66 Chevy trucks. I recently bought a painted factory pair on eBay, which included a printed instruction sheet entitled Front Bumper Guard Instruction Sheet Series 10 - 20 - 30 - 40, printed by CHEVROLET DIVISION General Motors Corporation. The instructions indicate drilling two new 5/8" diameter holes approximately three inches to the outside of the existing carriage head bumper bolts. There is a template provided indicating the same.
It seems drilling new holes is excessive when you can install the front bumper guards utilizing the existing front bumper bolt holes at the frame rails. I learned from this literature that drilling new holes is also an acceptable method per the factory literature.
