Yes it's analog. Out of a 91 Caprice Classic Sedan (civilian).
Where are you located? you could try it if you want to, but I suspect it's the Speed sensor or wiring issue.
I also have a FSM for my 92 Wagon, it has some diagnostic flow charts for the speedo. A code 24 in the ECM indicates a VSS problem.
I might also have a spare speed sensor you could try but I don't really want to sell it.
Hope that helps