Yes, trucks use a "DRAC" module that interprets/splits the VSS input from the transfercase, while car applications didn't, apparently that interpretation/splitting was handled through the ECM.
I have been looking at this for some time myself...205 w/VSS conversion, going to use the 90-91 speedo cluster. Could set it up to use the DRAC, but it looks like a conversion to a car ECM might be easier/cleaner/more rewarding than trying to wire up the DRAC, at least for me.