Thanks guys.
Street - we did them with VHT's 'Flameproof' header paint. When it's cured properly it holds up reasonably well, we've got a few places starting to flake already, though, as we didn't get time to do the full curing process.
We did the ones on the old motor with the same paint and it lasted a few years before it started to look bad. Had a lower-end ceramic coated set after those and they ended up rusting as well - I've just resigned to the thought of redoing every few years as a necessary evil
Here's the VHT we used -
http://www.vhtpaint.com/products/flameproof/