Hi JFerg,
I found a pic of the bike from the early 1970s. It was then fitted with Harley/Castle front forks, different exhaust, etc. It looks more "GP" now, but I think the fork, front wheel, and other details are still not quite right, even though the paint and plate are flawless!
Yes for such an unusual engine there's a good argument to have it out and running, rather than just sitting on a bench. The problem is that these composite machines tend to very quickly take on an identity that arguably they are not entitled to. I doubt the card at Sammy Miller's museum tells the true story of the bike.
Cheers
Leon