Speedometer drive gear

[62pan]

I purchased a 39 1/2ton pickup last year. I just got it where I can start doing test drives and I noticed the speedometer was off and the odometer did not work. The speedometer is now reading half of whatever speed I am doing. The rear is a 4.11 with the correct drive in the turtle. Speedometer shop says I have incorrect speedometer for the drive on the drive shaft. Did they make two different speedometer drives that go on the driveshaft or were there different ratio speedometer, 2-1 or 1-1. From photos I found my speedometer does look like 39. Speedometer shop is well known so I'm at a loss.