Re: Painting exhaust manifolds.
A dressing (Calyx brand) is what I use on my 396 manifolds. Works well, but I think if the manifolds are really scaly and nasty, it would not work as well.
I first tried Eastwood hi-temp powdercoat on then new repro manifolds. Scratched all to heck on the UCA studs during engine install; not a prep or application issue, as they were done with the assistance of a couple of friends who work for Eastwood. Found out that the high temp powder coat was very, very fragile.
Stripped the powdercoat, re-prepped the manifolds, and painted with Eastwood hi-temp cast iron gray. Still burned off eventually.
Bought the Calyx at Eastwood, and though it can take a while to work in the first time (on newer, relatively smooth castings), it does work well and will last for a season of cruising, as long as the manifolds were clean and don't get gunk dripped on them.
On the subject of the gasket replacement, was that because you had one or more leaking? Have you checked the faces of the head flange and manifold to see if they are straight? Though included in every rebuild kit, the factory did not install a gasket of any kind between the head surface and exhaust manifold. I have heard of manifolds that warped over the years, but I don't know how common it is or the percentage of factory GM manifolds to be warped just from normal heat-cycling/operation, or whether warpage is a result of someone installing them incorrectly later in the engine's life. On all the small blocks I have done/owned I have used headers, so that is why I never spent time checking factory SBC manifolds for warp; maybe someone else here can elaborate.
Anyway, if someone previously installed manifold gaskets on your car, it would be good to lay a straight edge across the mounting surface and see if you even need them.
69 'vert project big block/TKO 600 RR
68 'vert driver RS clone -- gone!