I just missed a set of alloy beam mounts on Ebay and I regret not buying them. I saw a set on there now for £50 and asked about them - they are mild steel. The seller recommends painting them with Hammerite but I reckon they will rub back to bare metal in the beam mounts and then rust heavily so I am staying away.
If anybody has a source for alloy ones I'd love a set. Mine are going in a race car so I don't really care about noise.
Charlie