I knew it was a control to switch tanks, but I couldn't see any way to fill them. That is a really sneaky way to hide more tanks.
I was thinking the instrument panel looked too nice to be original and now I'm thinking the whole thing has been replaced when the tach was added. The cruise appears to be a genuine OTC kit, installed after too. The black gear selector housings on the column should have been blue too and appear to have replaced originals that were prone to fading and cracking and the white letters losing their color.
Still a Super nice truck and I would leave the full wheel covers on it. Too many have the rally wheels now and this one stands out as original....