85mph and 140mph gauge "?"

i have both a 85 and a 140 gauge cluster, but my question is, can i use the 140 speedometer face and swap it with my 85? the reason im asking is the 140 cluster is pretty shot but the speedo is working fine. or could i just use a gauge face and use the 140 speedometer tranny gear? i dont know if this is confusing or not but i really want the 140gauge.
 
Take cluster apart, remove the 140MPH speedo unit. Remove needle, unbolt speedo from plastic frame and then carefully remove the speedo face off the plastic frame. Flip speedo over, drive out small roll pin on odometer and carefully reset mileage to what your car has. Drive the roll pin back in.

If you get to that point, then try to do the same with your 85MPH unit and swap them.