I made these some time back, they may be of interest.
The engine is a Standard12 1608cc, ported block skimmed head and a Newman cam.
1 1/4" SU's and a very long four branch manifold in 316
When I was an apprentice the old gent I worked with told me about a Coventry Climax he built with a beautiful copper exhaust, unfortunately it wouldn't pull the skin off a rice pudding until he put the old exhaust back on - something to do with the copper resonating and killing the exhaust flow he reckoned?? I don't know if it's true????