The mounting brackets you are trying to use behind the bumper are not for that bumper guard. The brackets you are trying to use are for the 1947-1953 truck grill guard.
The 54 & 55.1 bumper guard for 1/2 & 3/4 ton trucks { GM part # 986949 Group. # 7.828 } actually uses 4 mounting brackets { 2 behind the bumper that match the contour of the bumper & 2 braces that mount to the existing front bumper mounting holes}.
The original grey color on them was a lacquer finish & not primer.
