In reply to Matt Podd:
Wow, that's quite the undertaking. I've done the Hewitts but never bothered getting into the Nuttalls or anything similar. What criteria are you using for the tops (prominence, etc)?
Anyway, no idea how many Hewitts there are in the NP, but I guess it includes Glyderau, Snowdon group, Carneddau, Nantlle and Hebog hills, Rhinogydd, Arenig, some of the Moelwyns and Ffestiniog hills, Hirnants, the Aran hills, Dovey Hills, Cadair and the Tarrens.