You can probably get the tach to work but I just looked up the Term.-X wiring diagram and didn't see any VSS in or out. You gonna use a standalone trans controller? May have a VSS off that.
It has some outputs that can be defined to whatever you want. One of those things is a VSS signal. You can only do this on the "Max" version that has transmission control built into it.
Once I get around to attempting it, I will follow up with the details (assuming I get it to work).