Here's a URL which explains the whole process of changing a xsemi-auto to a manual.
http://www.claydons.demon.co.uk/beetle/autostick/
If you are lucky, the tunnel may already have a clutch tube in it (some do, some don't). It's the only "hard" part of the operation.
I have a 68 semi-auto which a PO converted to manual (the clutch tube had to be installed). Works just fine, except that the clutch tube has been set forward just a few mm too far, so it's hard top get sufficient bend in the bowden tube (too many washers needed at the rear end of it).
Rob
Rob and Dave's aircooled VW pages
Repairs and maintenance for the home mechanic
http://www.vw-resource.com