1967 to 1969 Barracuda Bumper Alignment / Fitting
You need stock measurements to compare.
The rear bumper should have a uniform gap of about 3/4" to 1", all the way around. I can't give an interior measurement of my bumper without taking it off the car, sorry.
My guess is that the problem is your re-pop bumper is to narrow. I have seen this problem before (on this forum).
Do you have access to a factory bumper that you could test fit?