To amplify Dave's post, Vetter prototyped the Hurricane on a '69 Rocket 3, which had both the leaned-forward cylinders and the twin-downtube frame. In '69, BSA and Triumph were still separate in the US. Don Brown was in charge of BSA in the US, he disliked the R3 (but still managed to sell more than Triumph did T150's), he gave Vetter a R3 and commissioned him to come up with something that'd more appeal to a greater number of US buyers.
>That is a nice replica made with the Rocket 3 engine.
To replicate a Hurricane from specifically a Mk.2 R3 is wa-aa-ay more work than just the engine, there are also many alterations to the frame. Trying to do it from a Mk.1 R3 is even more work. None of it impossible but, as I posted in response to Dave's first post, a huge financial pain for more financial pain when selling the result.