[asid61]

Originally Posted by AdamHeard

Embedding a quadrature output magnetic gear tooth sensor like 2363 (and 3847) did with a versaplanet might be an option.

http://www.chiefdelphi.com/media/papers/3165

Or give up some shaft length and do it entirely external on the shaft close to the output bearing.

You might be able to modify the GEM in a similar manner, or attach a gear to the output shaft and use a similar mod.