Classic/Antique Car Repair: 1950s BW T86 w/R10 tailshaft, speedometer drive, speedometer cable

Question
I have a 58 Ranch Wagon with an older T86 w/OD,  R10 tailshaft case and 292 T bird motor.  Neither original,  but vintage crrect.  I can't figure out,  among other things,  is how the speedo installs with the plastic gear and nipple.  The actual speedo cable unit installs opposite of the electrical unit/plastic gear with nipple in question.  I can get the electrical unit to screw into the case,  but how and where does the plastic gear w/nipple seat ?

Thank you so much for any info you can provide.  Is there a site I can see diagrams or manuals, that you know of ?  It's very difficult finding info.

Chris

Answer
I'm not exactly clear on what you are asking, but I'll make an assumption and try to answer that question;  if I have guessed wrong, post a follow up question to me and I'll try again.

You are installing an overdrive transmission, and you have located the place where the governor threads into the tail housing, and are looking for where the speedometer cable and drive pinion goes, right?

The speedometer pinion is driven by the same worm gear that drives the governor (which is what I think you mean by the "electrical device"), this means that it must be in the same plane as the governor, so it will be the same distance from the end of the case as the governor mounting, within 1/4 inch or so.   The hole for the speedometer cable is about 3/4 inch diameter (much smaller than the governor hole) and if this overdrive is from a 58 Ford, it is on the driver's side of the case.  There is a small threaded hole below the 3/4 inch hole for the retainer capscrew.   Since this setup is not original to this car, you will have to be very certain you have the right speedometer drive pinion for the worm drive gear to properly mesh with - if you don't, the gears will chew each other up.  If the speedometer drive gear came from the same car as the transmission, you should be OK.  
The same goes for the governor - the gear on the end of the shaft must be the correct one for the transmission.

The only other electrical device on the overdrive is the solenoid, which does not thread into the case, and is about a foot further forward on the case.

I hope this is the right question.

Dick