Agree, get the new pad for good measure. As for originality, Chrysler never did paint the fuel tanks, BUT on some years, the tanks did get a coat of undercoat on them, by observation.
I started looking at these things as I was seeking to discover the relationship of fuel tank color and hot fuel handling, waaay back in about 1968 or so. As if the fuel in the tank might be pushing fuel into the carb as the car sat on a parking lot in July? As this was back then, there was not a huge amount of readily-available information on the subject. Especially as it did not relate to a more powerful engine or such! BUT the "knowledge of the day" pointed toward basic fluid expansion/contraction as the ambient temperatures changed. Plus that the temperature of the roadway (which would radiate up to the car's undersides) could easily get past 150 degrees F on a July day in TX when the ambient temp was only 95 degrees F. In these conditions, IF you might be concerned about "wasting money", you didn't fill the tank to the gas cap unless you were going to be driving the car on the highway reather than soon parking it on an open parking lot (or a fuel spill could result!). Just common knowledge back then, especially on rear license plate filler neck locations.
At this point in time, many decades later, the default mode might be the clear paint mentioned above, or a similar bright silver paint (which would scream to those who might know what they were looking at "LOOK! I painted my fuel tank!") or for the "stealth mode", a coat of black spray undercoat on the underside. In the later case, just remember to NOT fill the tank completely full at night, when it might be cooler than at High Noon the next day.
Just some thoughts and observations,
CBODY67