I recently cleaned heavy paint accumulations off the cowl tag and the VIN plate of the '56 Nomad I purchased last year. The paint was similar to yours, so thick it was difficult to read the stamped characters. I first masked around the plates as carefully as I could with good 3M masking tape, then added a second layer and taped a few inches from the plates. I tried several milder solvents (mineral spirits, xylene, etc), but nothing worked very well until I used lacquer thinner. I folded shop towels up to get several thicknesses in a small area, then soaked that in the lacquer thinner (not dripping wet, but 'wet')... I had to replace the shop towels several times repeating the process until I had all/most of the paint off the plates. After removing the masking materials, I used compounds to clean the plates and the surrounding areas.
In your case, if you end up cleaning all the paint from the cowl tag, you could probably lightly spray 'firewall black' over it to simulate the factory application...
