I've been using a Hi-Temp paint that my muffler shop buddy clued me into some years back. This paint is by plasti-kote #HP-11, says resists heat to 1500 deg.

First you scrub or clean the pipes with a scotch brite greenie pad. Spray on the paint, run the vehicles so it gets hot and dry. Then next day after paint is really dry take an old towel or clean dry wrag and polish or 'burnish' the pipes til shinny. I've used this method on a couple cars, last a long time.

Also must good shops today use aluminized pipe only.

It's easier to get forgiveness than permission!
1946 1/2-Ton Chevy
1953 Chevy 3/4-ton Factory Stakebed