· Chief Cook and Bottlewasher
Sounds like you have got your solution. If you keep sanding to bare metal, you will have the POR still in the stamp indentation and the numbers will be very clear. Leave it that way through the inspections that you need, then paint it up to avoid rust. Or paint it with clear so that it stays very visible. Before you sand it down to bare metal, tape off the rest and clean and neatly done area.
When I painted my frame with POR 15, I happily painted over the serial number. I am pretty sure they will want to verify this number against my certificate of origin when I am eventually ready to register the car. So how should I go about revealing that serial number without damaging the stamp?
I was thinking about a wire wheel, but I am still thinking that could damage the serial number since it is stamped so lightly.
Edit: Nevermind, I guess I didn't slop the paint on too thick because I was able to make it out. I did a light brush with sand paper and it stands out even more.