Thanks TMers. I used a combination of all ideas.
1. Remove the surface rust from the manifold plate with a combo of wire wool, sandpaper
2. Clean the pipes and welds with kitchen foil and Solvol.
3. Mask up manifold pipes, studs and nuts
4. Treat manifold plate with Kurust.
5. Remove masking tape and clean brass manifold nuts.
Excellent results - just a well cared for look without going over the top.
PS. Don't know how long the Kurust matt black look will last , but definitely worth a shot.
