I would advise on a Raceland manifold - which you can find on Ebay and get a Powerflow custom made middle and rear box, this is really a nice set-up and the noise has a nice tone....
Mk1 GTI exhaust will not fix unless you want to start cutting and welding which isn't worth it considering the custom set-ups you can get these days and the prices...
Have you looked at Jetex exhausts or call up GSF - they do VW standard ones - which are great quality and price..
I would call up Ian Birch at
www.pipewerx.com custom exhausts - Ian knows more about VW's then most in this country and is well known for his skills - there was a 4 page review on his custom exhaust company in VW mag the other month - they know there stuff...
I am sure we discussed this in length in another thread about a year ago - so try search on this site as well..