Can't help, Mike. But I love the centre piece. The little mat displays the mainifold & carbs beautifully. All you need is a couple of daffodills down the throats.
I have tried this, even at one stage setting up the Norman as a centre piece, but my wife does not seem to share my imagination.
Seriously though, would be keen to see how you go with those cast parts. Something I have always wanted to do, but the foundry down here isn't into smaller works & the one up North is just that, up north & too far away.
Rob J