Well, I found part of my answer.

Apparently to get rear-curtain synch you simply turn on an AE prism AND use an SCA unit. According to Tamron/Bronica this is the way you do it. The SCA adapter can't link with the electronic shutter so when you turn the AE prism system on, it will keep the shutter open and THEN fire the flash.

Which makes me wonder at what point in the shutter cycle the flash is triggered.