@dhcod: Are you certain it is the arm not the cartridge that is responsible for the mistracking? The current London’s are better in that regard than were the Decca’s, but tracking remains the design’s major failing. The SME has long been considered to be a poor match for the cartridge; something about the huge amount of mechanical energy it puts into an arm causing the SME’s knife-edge bearings to "chatter" (that’s why adding mass helps).
Arms popular amongst the Decca/London cognoscenti include the Sumiko MDC-800 ("The Arm"), Zeta, Hadcock (and other unipivots), Mission Mechanic, Fidelity Research, Helius Omega, Well Tempered, linear trackers including the Eminent Technology, TransFi Terminator, and London’s own. Art Dudley even liked the London Gray in a Rega 300, but he’s not a Decca nut. There are some older Audiogon threads on the same subject.
If you really want to go all in, get yourself a Townshend Rock, THE table for the Decca/London!