Jeff
Ouch, I can see this becoming a bit of a touchy subject ...

Now, if you (or anyone) wants a trike due to 'physical' problems, you'll get "thanks for choosing a Triumph" BUT

.. if you want to trike a BA or Speedy just because you can, you'll probably get strung up by the Jacobs ..

If you simply MUST have a trike, then obviously anything is possible and I've seen a company (some time ago) whose slogan was (very original this) "We trike any bike". Kinda catchy eh?

I believe a Gold Wing kit is something like £20,000 plus the donor bike!!

I've seen a Rocket III (it even had Ray Birch on it!!) but an America or Speedy? Good luck?