so here was my solution - essentially i made 2 of these. The outside diameter of the aluminum stoch i used was 80mm (about 3.1"). This seemed better than the racetech collars, as the support more of the spring, and the flange engages more as well. One of the pieces I made accepted the bottom collar-washer on the shock and one accepted the top collar on the shock. I felt that retaining the steel collars was useful, vs having aluminum alone. shock went on without a hitch, and... significant improvement in ride and handling. preload via these pieces is about .5" I still have some limited tuning on the shock to better match the higher rate, but i am satisfied.
BTW.. I am not machinist, and the lathe I used was sloppy as all get out.