[142 Guy]

Just a heads up. On my 1971 142 E (North American market) the bumpers are two part. There was a thin skin on the surface formed over an aluminum core.

I removed that surface skin long ago; but, my recollection was that the skin was polished aluminum. I cannot advise whether it had a clear anodized finish or a clear coat finish; but, being aluminum it would have required some type of finish to keep it from developing that common dull aluminum oxide. If my memory is correct about the skin being aluminum any polishing will further damage the remaining anodizing / clear coat putting you on a maintenance treadmill. You have the option of mechanically polishing the skin to remove all the blemishes and then clear coating or having a clear powder coat applied (after removing the rubber strips for the curing process).

As I mentioned I removed the skin because in my case the skin was in really bad condition and had already started to separate from the core. After removal, I found that the core also had some serious surface pits so simple polishing and clear coating was not an option. Once the skin starts to separate it becomes wonderful trap for moisture and corrosion. I initially just sprayed the aluminum cores in a satin black (period correct for the '80s 'tuner look'). When I did a complete resto on my car I considered having the bumper cores sprayed is a two part 'chrome' powder coat. Because of the pitting on the cores I would have to use a high temperature filler to withstand the high cure temperature which was extra effort. Since the car was being re sprayed I elected to use a conventional filler and color match the bumpers to the car. The chrome powder coats are good; but, you definitely will not mistake them for chrome or highly polished aluminum.

I can't comment on what your 2K polyurethane paint will look like; but, if you have corrosion pits make sure you sand them out (fine pits) or level them with filler. Nothing amplifies poor surface condition like a new glossy paint coat .

I am not so sure about anodizing being a cheap and easy process in the context of the home workshop. Setting up for a piece as large as the bumper and the amount of chemical required may not be cheap for a one or two part fix. I used to race sailboats and was perpetually doing touch up on the anodizing on aluminum spars and like because of surface damage. Those repairs were for surface protection and definitely were not cosmetic. Anodizing is an inexpensive and easy treatment when you have a large production run and can dip the parts in large vats of chemical.