I follow your thoughts on keeping the fountain & over flow.
Would fabricating the riser pipes and fountain arms out of acyclic tube be an option? With acrylic riser pipes and fountain arms there would be minimal metal contact in the original fountain head.
You could use clear acrylic and use copper krylon spray paint to get a functional reproduction.
I can still use the original riser pipes by just coating them inside and out with clear epoxy or using vinyl tubing on the inside so I wouldn't need to use acrylic. I just need to figure out how to coat or line the inside of the fountain arms since they are so small in diameter.