Re. the mystery pipe, I've discovered that that it's a water pipe for the carb, rather than a vacuum pipe. Didnt realise the manifold had a water jacket!
Martygf- havent yet got round to using the rebuild kit, I've been too busy to spend much time on the car unfortunately. Will let you know how I get on.
Lucio - I would love to take the car to somewhere like DTR, and if I knew it would only be an hour's labour then that would be fine. My worry is if the garage I take it to needs to spend 3 or 4 hours on it then it's going to cost mega-bucks. At the moment I'm beginning to feel that it's going to have to go to a garage though. Hopefully the rebuild kit will help in some way, and I'm also going to clean the inlet manifold and heatshield, then reassemble with new gaskets.