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Tony,
For eyepiece projection, from an optical design perspective there's an awful lot of merit in using an eyepiece that is more or less symmetrical front-to-back, and which is also suited to the field curvature of a Newtonian. The simple Plossl is the obvious and almost perfect candidate as it's just two Plano-convex doublets with the crowns facing.
In some respects a 20-50 mm camera lens - reversed - may also work if you have the rings and adapters to fit one backwards as camera lenses in that range are usually Gaussian designs.
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