Speedometer gear question
 

I am trying to recalibrate the speedometer in my 75 Firebird 350 4 bbl with turbo 350 trans (inherited from my grandmother who purchased it new in fall '75). Years ago I replaced the 2.76 open 10-bolt rear with a 3.42 10-bolt posi rear. Anyone out there know what amount of teeth the correct speedometer gear should have?