I've never had any paint stick to an exhaust manifold for longer than a few days, even the "high heat" stuff. Your options are to ceramic coat it, or use this: https://www.eastwood.com/calyx-manif...iABEgLLm_D_BwE
I've used it on multiple manifolds. It last for a long time and re-applying is easy.
61 II 109" Pickup (Restomod, 350 small block, TR4050)
66 IIA 88" Station Wagon (sold)
66 IIA 109" Pickup (Restomod, 5MGE, R380)
67 IIA 109" NADA Wagon (sold)
88, 2.5TD 110 RHD non-hicap pickup
-I used to know everything there was to know about Land Rovers; then I joined the RN Bulletin Board.