I would not be scared of it. I have used “Red Kote” in several vintage Honda 3 wheeler tanks and works great. I hear that POR makes a great tank restore kit and plan to use it on my next tank that needs it.
On another note, How much different are the tanks from a Buick? I know the filler neck will be different but if the rest of the tank is the same maybe you could find a good used Buick tank and swap necks?