Search the archives cos there's plenty on this topic. No template available from Caterham when I bought therefore cut hole carefully; I used a Dremel. To remove the old (one piece) 4:1 manifold: disconnect battery, remove chassis strut, remove lambda probe, undo & remove all manifold studs, lift out manifold. I removed the water rail as well but may not be necessary. Then offer up each primary & trim the side skin as you go.
Mick