Its the Load spark advance for the Ford EDIS spark units, 4.0l OHV would use an EDIS-6, with Crank sensor and coil pack
Its an autonomous system, you can start and run the engine just with this and some fuel
But....................
EDIS can only do RPM spark advance it can't do "Load" changes for spark
The EFI computer did that because it has Throttle sensor, MAP/MAF sensor, and air/fuel mix info
EFI computer was connected to EDIS via SPOUT wire, and that told EDIS how much to advance or retard spark timing from RPM timing based on engines Load at that time
Vacuum advance on a distributor was for Load Advance, does the same thing as EFI computer or MEGAJOLT/E MK2
You need a MAP sensor for sure, and a Throttle sensor if you want better throttle response
But MEGAJOLT/E MK2 looks to be tuneable, which you will need running a carb because thats an unknown as far as air/fuel mix
So you need to tune the spark curve to match YOUR carb's air/fuel mix