I have the engine bay down to the metal and getting ready to paint. I'm wondering if I should use epoxy primer for this area, or an engine paint such as the Rust-Oleum engine primer/enamel that is made for high temperatures?

I'd treat with Ospho or similar if you haven't already, and then hit it with 2K epoxy.

You can get phosphoric acid products at a home store, which will convert micro rust to a paintable surface and promote adhesion. Be sure to rinse and dry, clean with a wax and grease remover before the 2K Epoxy Primer. I highly doubt the factory used a special primer in the engine bay, so epoxy would be a good choice.

Concur with Brent. Ospho and 2 part epoxy.

Would RustMort do the same as Ospho?