I used Goodmark 1/4's five years ago on my 73 Challenger, and yes the side marker light recesses were "iffy". The holes in the 1/4's for the light socket & stud needed to be wallowed out and masssaged.

The other "iffy" issue was the hole for the gas cap. Actually, there was nothing "iffy" about it.
I found out after the car was painted that the recess for the cap was apparently designed and stamped by a one-armed blind man... I had to go to my local Mopar "boneyard", and have him torch a "hole" off of an original 1/4", and I put that piece in on the trunk side of the 1/4.

Might as well take him your gas cap, either the stock flat one, or the "flip-top", and check it at the same time that you check the marker lights...