Are both of these items on 1931 Coupe painted "Gloss" black?

The core on my '31 coach is flat black, the tanks are gloss black, the fuel tank is gloss black at least after the restoration and were before, but that may not be correct

Paint your radiator with the paint used by radiator repairer's.
It is specially designed to tranfer heat from the radiator correctly.
You can purchase it from Eastwood Co. for $14.99

Originally the gas tank was tinned steel. Outside just like the inside. The coating would protect the tank from corrosion. Since the frame was dipped way before the gas tank was installed there is not reason to paint the tank. I have yet to find one that was painted on the surface up against the frame on an unrestored vehicle. It is common for the tanks to be painted black during restoration.

The radiator was painted with a heat transfer paint thinned with gasoline. It only puts a light coat on the core and tanks. Gives a matte or semi-flat surface.

On my original 1932 Special Sedan, when the gas tank was removed for boiling out and cleaning, the top surface of the tank (the part against the frame) still had the original finish in place and the finish was black Japan enamel. Other areas of the tank still had some black paint remaining as well.

I may be that some were painted or coated. Does not make sense to paint them when the tin coating on the steel protected the tanks, just like they did up until they switched to plastic tanks. Same protection in brake lines.

I just checked the gas tank on my original 1932 Special Sedan to refresh my memory. Actually, there is a fair amount of original black Japan enamel still remaining on the tank. Portions of paint are remaining on both ends of the tank (besides on the top as mentioned previously) and on the bottom of the tank as well. Also, the tank is plain steel and it was never tinned.

The original gas tank on my 1930 Chevy was also painted with black Japan enamel over plain steel. The tank was not tinned.
My '32 was manufactured in the Oakland factory and my 1930 was manufactured in the Kansas City factory.

A couple of filmstrips in my collection show the gas tanks on the vehicles featured as being painted black. I suppose it's possible that the gas tanks came both ways....either tinned or painted.

I am not saying your tanks were not painted but just be aware that the tin coating will age to a black color if any H2S or other similar sulfur compound. Also soot or smoke will often blacken the original coating. I can send you numerous examples if you wish. Just pay the shipping.

Ya, I checked very closely and the tank does not have a tinned coating. The original black Japan enamel on the gas tank of my '32 has some runs and sags in the paint. There is also a large built up of black paint on the end seams as well. The paint will also flake off with a sharp object like a knife blade. It is not a tinned coating that has turned black with age. The exposed bare metal on the tank is definitely plain steel and not tinned.

As I mentioned earlier....the gas tanks probably came with two different coatings.....either painted or tinned.