Hi, just done the same conversion on my 4x4 '96 hilux and had the same problem. Went to a breakers yard and swapped in a gauge cluster from a hilux surf/4runner as these have the electric speedo and also rev counter. Just have to bear in mind that although the plugs on the back are the same the wiring is different so had to swap a few wires around PITA.
Cheers Chris.