Hi Bill, thanks a lot for this.
I did end up cleaning the surface of rust and oiled it like a pan but a few issues arised. Mainly smoke as the oil got too hot and burnt. The house got filled with the stuff. The kitchen gets filled with smoke when dealing with just a pan, but this stove surface is about 15 pan sizes!

In addition to that, since the stove runs when doing a slow roast for 3+ hours all the oil is cooked away and gone, meaning reapplication every time and a lot of smoke each time. But maybe that is just the oil I'm using?
Back when I was a kid I worked at McDonalds and we had these big grills for cooking meat. I guess they were made of a different kind of metal. Anyways the metal never turned black, and I don't recall there ever being smoke like this. I don't think they ever applied any vegetable / seed fats to the surface - I think it was all just fats from the meat.