Does the OD tranny require a shorter drive shaft?

["Andrew Lundgren" <lundgren@iname.com>]

I'm working out the details of getting an O/D tranny for my car and 
have a few more questions.

I have a '70 B, non-OD

This tranny is off of the later (non-crash box) car, it has the OD 
switch on the knob.  

Do I need a new speedometer or just the gear on the side of the 
tranny?
Do I need a shorter drive shaft?

Anything else I am missing here?

Thanks!