Speedometer adapter

I believe you can buy a speedo that works with GPS. No cable required.
I would have to rework the dash cluster and not interested in that.
Yikes! Thanks Dave999, I almost forgot about this:
More Information for WVE 5S4686
1992 D150.
Screws right on to your speedo drive and generates a VSS signal, should work for your current speedo?
This looks like exactly what I am looking for