Success! I had installed Sierra GM on my 'real' macbook pro, so I had a copy of the GM seed in my MAS 'purchased' tab, so when I agonized over how to install it on my big hack rig, I says why not just go for it and see what happens:
- Downloaded from the purchased tab
- Just ran it when it finished downloading (NO createinstallmedia)
- Took less than 40 minutes
- After the last restart, I had an almost perfect Sierra 10.12 (16A322) system with all my apps working (including TotalFinder)
To get audio working I had to use toleda's audio script at II.1.1. in
http://www.tonymacx86.com/threads/audio-realtek-alc-applehda-guide.143757/#post886744.
I lost my little asepsisctl utility (kills those nasty .DSFile's) as well as a patched 'old' style DiskUtility.
Happy camper here! Thanks to Tony and the whole gang for your continued support.