It was around the time of digital cameras that trigger voltages dropped to around 6v. They were slowly lowering before that, but a 1976 Sunpak 611 is supposedly somewhere between 100 and 200 volts, with some reports saying it's on the high end. If the Sekonic doesn't mention anything about accepting high trigger voltages, I would assume it wouldn't. That's a selling point, and usually if they spent the money on parts designed to handle such voltage, they'll advertise that.
I have used some old Novatron systems with my digital cameras in the past. I have no idea of their trigger voltages, as I haven't measured them and they changed a lot over the years, but I assume they're quite high. I just use wireless flash triggers with them, and that prevents any chance of complications. I use Phottix brand triggers, as they're cheap and will accept very high trigger voltages (and work well), but there are other brands that will do this too, you just have to check the specs. This would allow you to run the flash chord off the camera, or use a third trigger for the meter, and keep the high voltage from the flash off your meter and camera.