I did this front and rear on my '72 'Cuda. It was a pain. I'm pretty sure I purchased both bumpers from Unlimited. Neither one fit just right. They were too narrow (vertically) and too long (horizontally), the ends didn't tuck in right and the crown was off. I cut both bumpers in half vertically and horizontally and used aluminum straps pop riveted to the four bumper pieces to get the correct spacing. Once I had the pieces in the proper locations, I fiberglassed everything back together and then did bodywork to make them smooth. I sand blasted the chrome off of the two rear bumperettes to fill in the bump outs in the lower valance panel and painted everything. I bet I have 40 hours into those bumpers.

If I was to do it again, I'd just replace the front bumper and I'd ask around to see who makes a better product as a starting point. And I wonder how much those "elastomeric" bumpers weigh. Maybe you slap a pair of those on and save a bunch of weight?