Correct speedo gears

Hey All,
I have a '97 Cobra vert which is mainly stock except for a few bolt-ons, one of which is 4:10 gears that I had installed last year. My problem is that no one seems to know the correct speedo gear that I need . Can anyone help me with that ??? From what I can figure , I now have about a 20% error in the readings. I don't care about the mph, but the odometer reading is adding miles I don't want.
Thanks in advance, Tom T

In my opinion the best way to correct your speedo is to get a Speed Cal. It is my understanding there is no perfect speedo gears for 4.10's
http://www.americanmuscle.com/speed-calibrator-94-04.html