I'm wondering if clay bar would help get some of the dirt and compound out of existing paint. After compounding a very oxidized car, I had to clay bar it before moving on to polishing.
The frame and K-member on 67 and newer are wider than early A-bodies. I think it’s worth a try fitting the 67-69 bumper. Another option is a Camaro bumper (I won’t tell anyone).
What car are you working on here in the PNW? There’s enough cars, people and wrecking yards that you could get nice used trim. Or, you could set up shop and be the go-to guy here. A lot of the aluminum parts have a protective coating called bright-dip which needs to be stripped off before you...
Or, you can narrow your stock tank. Cut a couple inches out of the right side so it sits centered in the car. You can also look at other tanks like 62-65 Fairlanes, but you would have to cut out the spare tire well.
Clay bar will remove surface contaminates in preparation for buffing. What could it hurt to learn on a car that has dead paint anyway? It's going to look better, even if you burn through in a couple spots.