Hi,
I'm not an expert but I can't see why 90bhp isn't achievable from an NS with big bore, porting, carbs pipes etc.
Someone posted a Shepherd NS500 on the NS400 forum which had 70bhp, but even 80s 125s can be made 30bhp - so you only need to match that to get 90 from the NS.
I think it's got to be down to the lack of numbers of people tuning the NS. ie if someone like Mark Dent got hold of one, and did all the development work...
I *nearly* did the conversion to 2 CR barrels on the NS, but it was too much work versus the 500. I'm now planning a really daft barrel swap, plus stroke enlargement, not sure if it will be feasible yet, but if it comes off it will be good.
Happy new year!
Mat.