Ensure the header pipe is secured at the lower end in front of the header pipe output top the catlytic convertor input.

The bracket that hangs from two car right side bellhousing bolts, ensure you have all the hardware to support just up stream of the header pipe out union.

If you are concerned about rust, you may want to use copper alloy of like strapping to ground the exhaust to the unibody to slow exhaust systems corrosion. I forget the name of the braided copper alloy or soft stainless strapping, yet the strapping will break auch as when you have an accident and the exhaust rips off.

Inspect the headerpipe for rust around the welds. The most critical weld is a the 2 to 1 runner union.

There is nothing wrong with painting or finishing the manifold and header surface. You have some kind of thermal paint. There exist other thermal paints for use on exhaust. I've seen these yet do not know the brand.

Good luck on the newly installed manifold. New exhaust mainfold and cylinder head gaskets and new exhaust manifold to cylindr head gasket studs that are OEM Volvo is a good thing!
--
Beh.

While wrapping the pipe will retain heat, a higher temperature may accelerate oxidation. Keep in mind that a LOT of water is a byproduct of a gasoline engine. The condensed water vapor that you see on a cold day is equal to the water vapor that comes out on a hot day as well.

It is also possible that a higher exhaust temperature may cause other problems - overheated cat, melting something, etc

Our VW 411 had helicoils in the nuts on the exhaust manifold, making removing it a quite easy.

Perhaps you can get some hardware that won't rust up to make the next replacement easier.

I have a tailpipe cutter that has 4 cutting wheels and a screwdriver handle - you only have to swing it a little over 90 degrees to cut a pipe - manes exhaust work a snap.

I would get it very hot (like drive up a steep hill for a while), then measure the temperature. I think some manifold paint is rated for like 800F, if I remember right. I wonder if a splash pan on the engine would help - or if washing road salt off the downpipe occasionally would be enough.

I think it will just burn off,,,maybe you can wrap exhaust https://www.designengineering.com/products/heat-control/exhaust-wrap/