Joe,
Take a look at the exploded diagrams for your GT on the SIP Scooter web site - they should show you what the standard fittings are and what goes where...
http://www.sip-scootershop.com/ersatzteile/Maxiscooter
You might need to pick through these layouts - SIP seem to lump a lot of modern Vespas together like the ET4, GT etc.
If that's no good, try the equivalent on the Suttons web page...
http://www.vespaspares.co.uk/spares/epcPageList.asp?ModelID=1323&uID=0
If you're buy from either site, check prices and shipping - Suttons ship from Milton Keynes, SIP ship from Germany.
On either site you should be able to see pics of shocks. The SIP pics are better quality and can be zoomed to check small details.
Good luck with it