Sll god - status says it is out for delivery . PHEW.
Matt, that is what I thought, and tried it a few days ago. Yes, the adapter lets it fir the hole, but in no way will the azimuth secure, as the GP azimuth peg is further BACK toward the hole, and the SX is further away towards the rim, and a different shape. The azimuth screws don't even touch the peg.
I thought to use the half pillar, but no way either - same deal.
So, a GP tripod fits a GP series head, but not SX series head. An SX series tripod has a head adapter that makes a GP series head fit it. There probably is an adapter from SX head to GP tripod, but that no longer maters