Put a Galbreath head and Nelson plug on 'em and you'll never blow another plug, either. Plus adding a few hundred rpms.
Of the Norvels, I have 2 .061s and 2 --or 3, I'm as bad as you--.049s. 2 VA .049s that really go, and a Brodak Mk 1 .049 that I've never run. Plus a couple of Black Widows, and half a dozen Cox production .049s. Too many engines, I can't run them all. Can't quite justify buying a new Brodak .061! At least to wifey.
--Ray