Thanks for your clarification RE clock phase.
The schematic you excerpted is not the FR6M I’m working on. Mine implements the clock divider in a DN811 quad flip flop IC, not in discrete transistors. It also very definitely has a momentary start/stop pushbutton.
RE using start/stop pulses rather than sync gate, I plan to wire the toggle switch to select either the pushbutton or the sync gate edge detector to pulse the start/stop latch. The only state alignment issue one could run into is when switching the FR6M into MIDI sync mode. Requiring the user to do this only while the machine is stopped seems like a small price to pay given that I’m forced to work on this circuit without a schematic and the start/stop latch is not easily accessible. Additionally, I can’t think of a use case where one would want to switch between internal and external clock in the middle of a song. That said, if you could find the right schematic and share it with me I’d be happy to reconsider!
I’ll post my solution when it’s done.