It is a stock replacement tank, 1970 Cuda, p/n CR8E, They say stainless and it "looks" stainless.
If I were to modify it with an access hatch, to use the HydraMat, I think the costs would get out of hand.
A small added sump shouldn't be too expensive. I want to use an electric pump, Carter 4601HP, so a low pickup is desirable.
Holley makes several Hydramats that can be attached to the factory style pickup tube and passed through the stock sending unit opening.
https://www.holley.com/products/fuel_systems/hydramat/hydramats/