I took the speedo gear housing and gear out of the BB 727 Im working on. The gear is black plastic with a metal shaft the slides into the housing. The black plastick gear has a 29 code on it, the metal housing that it slides into has a series of numbers stamped on it: 39-45 32-38 26-3

What do the numbers tell me on each piece?

The 29 is the tooth count. the numbers on the housing are what you need to point to the mark on the trans. Each set of numbers equates to the number of teeth on the gear. Info from the tech site here. The tech link is at the top of this page.
http://www.moparts.org/Tech/Archive/auto/12.html

http://www.moparts.org/Tech/Archive/auto/21.html

What Stump said and there's another number on the end of the "26-3" so it is 26-32 (teeth)

cool thanks guys Ill follow the link and see what applications these will work in as I probably cant use them on the car my 727 is going into so Ill sell them

the tooth count is determined by your rear gears.
matching the tooth count to your ring gear i.e. 32 / 3.23. 35 / 3.55 etc will
usually get you close enough with a tire close to stock size...

You align the markings on the die-cast part (notch to dot) for the gear you have, i.e., with your 29 tooth pinion, you'd used the 26-31 range.

Rick

The housing is an eccentric, so the different "positions" move the gear closer/farther away from the speedometer drive gear on the output shaft (you rotate the housing to a different position to a mark on the tail shaft housing). This is because the gears are larger/smaller depending on the number of teeth on the gear. You want to align the corresponding mark on the housing with tail shaft housing mark for the correct number of teeth on you gear so that the gear is positioned properly to the output shaft speedometer drive gear (not too close, not too far away, just right). Put it in the wrong spot and you can damage the gear or have a non-functioning speedometer.

Chuck