Like others, My 70 Mach 351C has an Electronic Control Module to the left of the fuse box.
The large hose goes to the top port of the Vacuum Control Valve (3 port water jacket vacuum valve)
The small hose goes to a ported vacuum source on the carb
This system should have a speed sensor and a thermal switch - I can't find either. It looks like the speed sensor should go to the spedometer or be in line with the spedo cable (I don't know), mine goes no where - it is unplugged. The thermal switch connects to the grey wire (through the harness) and to ground. I may have one somewhere but I can't find it.
It looks like this system should work with a dual or single diaphragm distributor. My car has a single but I'm not sure if that is correct.
If you know anything about this system or have a 70 mustang with a 351C that you believe to be correct, please contact me or leave a post.