I'd be very surprised if there isn't a modern adhesive strong enough to stick body panels together, however it probably all depends on whether they're thin modern metal or Triumph metal...
I'll watch this one, given that I can't keep the stainless trims on my GT6 bonnet down - they insist on lifting at the front, just an inch or two, so any adhesives that I haven't used so far will be next on the list. (Still covered in Tigerseal from yesterday's attempt, and they lifted off immediately after 24 hours setting time, once I removed the straps tapes and weights holding them in place.)
(I've just edited this as I've had 50% success... one down, one up!)