From what I have seen the Ford computer isn't real fussy about the VSS signal it gets. Many people run without one completely.
The only logic I am aware of in the computer regarding vehicle speed is a little coast down stuff (coasting down a hill against the engine and it stalls at the bottom). Keeps a basic IAC setting until it knows you are completely stopped as opposed to seeing high engine speed and no throttle and backing off the IAC to nothing. Then when you do stop there isn't enough IAC to keep the engine running.
The second is some hidding timing stuff that kicks in a 100 MPH, or with the Stak sensor 267 MPH.
Unless you just have to spend the money, try wiring the Stak sensor straight to the EEC. If you find the timing stays too advanced over 267 MPH or you have a stall after a long coast, then look at spending some money on a signal multiplier.
As far as wiring it, I think you have it wrong. The EEC puts one of the signal wires to ground, the other goes to the input. That should be completely compatable with the speedometer as well. If the speedo has one signal wire, it shares the same signal as the EEC gets. If the speedo has 2 wires for the sensor then they both go to the sensor (and one of them is grounded for the EEC)
The sensor has 2 wires, you don't give one to each. The sensor is not internally grounded. It would be unlikely that either would work at all. Well the EEC would probably work, just not care about the lack of signal.
It's from a Jeep Wrangler Rubicon transfer case (NP241). Metripak was a reference to the type of electrical connector on the end of the sensor.