Drive gear Yes. Driven gear No. You want to change the driven gear. You will
need a 23 tooth speedo gear Not clear why you want to change the drive gear
unless you are looking for extreme accuracy..

Try http://www.steeda.com/store/-catalog/speedometer.htm

You might do the same thing I did when I changed my 2.73s to 3.27s.

I didn't know if my '91 5.0L AOD had a 7 or 8 tooth drive gear, so
I asked the mechanic to pull the existing factory speedo gear and tell
me what color it was.  I had bought three speedo gears from my local
FoMoCo dealer, all close fits to what the Steeda page told me.
When he said "gray", I knew I had an 8 tooth drive and had him
install the 3.27s and the purple 21 tooth driven gear, then returned
the unused speedo gears for credit.  I do a -lot- of highway driving
and the 3.27s and engine RPM were happy with this combination.

To confirm the correct driven gear, borrow a GPS and see if it agrees
with your speedometer. My speedometer and GPS read within 1% of each
other. (Probably the needle width and parallax error on the speedometer).

Don