Hi, Peter, and welcome to the Thorn Cycling Forums; nice to have you aboard!
Yes, you did just fine in placing your "wanted" query here. I'm hoping things will move along quickly for you so you can soon have the bike of your present dreams and sell the one of your past dreams. The Triumph Thunderbird sounds nice, and you'll be getting another wonderful "bike" in return. RTs ad RSTs are wonderful machines, and you won't have a moment's regret once the deed is done.
You've taken a great first step toward your goal by listing here, and I'm guessing it won't be too long before you get the lead you seek. Don't forget..SJS Cycles' (Thorn's mail-order retail arm) own listing on eBay and on the SJS Cycles site, usually here:
http://www.sjscycles.co.uk/clearance-zone-dept756_pg1/ eBay is another source of used (use the search string "Thorn Bike" to get a lot of listings quickly, and don't forget to check the Bikes For Sale board right here on the Thorn Forum. All are good sources for finding a bike that will suit your needs to a "T"(horn).
All good luck!
Best,
Dan.