It might well be worth fitting a civvy camshaft . The WD/NG was fitted with the sidevalve one . With the civvy one , either NG or NH you will have a very usable bike . I think that my NH was one of the best bikes I had . The Carburettor may also be on the small side , and an upgrade to a civvy bore would not be detectable . I have figures somewhere . There is a very active Ariel club . All threads on Ariels were BSF , except for studs into ally , which were Whit / BSF.
On today's roads it is neccessary to have a reasonably competitive performance . Even the NH was an extremely tractable bike .