First, I'll get this out of the way. I think the pipes are art and look beautiful. As they say, art is in the eye of the beholder (a very under-appreciated truth).
As for the overall bike, i highly doubt the builder had a nice Rapide or Black Prince (I don't know what engine) sitting around annoying him and decided to take the engine out and slam it in a Triumph frame. Clearly, he had an engine that needed a practical and affordable home and executed the transplant very well, and well beyond my own patience, budget and, maybe, skills.
Richard L