Thanks for the replies. I’m familiar with each of these perspectives, which is why I find it so interesting. I’ve cleaned up chromed steel before, and this is nothing like that. I’ll have some more pics in a day or two. My first day looking at this is documented here:
https://hondacb750k5.wordpress.com/2020/04/26/foot-parts-prep/After the post above I did some more widespread sanding. I then found that this applies to all of the supposedly chrome plated pedal parts: shift, brake, kickstart (including knuckle and pin). They can all be ground, filed, sanded apparently indefinitely and polish up to the exact same look. I even deepened the grooves in the foot grip to restore its bite after years of wear.
The chrome content of the metal appears to be uniform. It rusts where in regular contact with iron, and where it collects (often very salty) road water, such as under the pedal. It’s magnetically attracted, which is certainly possible, though I didn’t expect it. None of these suggest it isn’t stainless. I just find it hard to believe Honda would have done this. If they did then properly polishing up the surface restores the metal to its original corrosion resistance (getting the surface chrome density back above 12%).