Tag Mount on Standard Bumper

[crawdad]

The rear bumper on my 85 is a standard type, but it didn't come with a place to mount the tag on it. I took the tag mount off of my old 72 bumper but it turned out to be too wide by about 1/2 inch. I then ordered one from LMC but dang if it isn't about the same size as the 72, still about 1/2 inch too wide. Are all of these standard bumpers about the same size in the tag mount opening. Do the tag mounts have to be beat in with a BFH or something? I've got to get the tag out of my rear window. The state patrol let me go last time cause I told him I had one on order. Don't think he'll be so considerate next time. Any help or ideas appreciated