Let us know how that turns out.
I did my manifolds with the regular "metal mask" that looks like cast iron.
I primed one and din't prime the other.
I have a feeling it won't last.
The unprimed one is starting to show some rust already.
I had the same thought about the paint you mentioned on headers, since nothing else really works.
See if your local paint and body supply store can get it for you.
Mine is the same price as ordering from ebay, or POR 15, but there is no shipping charge.