MGB '79 OD conversion practical questions

Hi,

I'm going to start an OD conversion next weekt. It's a gearbox with blue label which should fit my '79 USA MGB.
Where is the OD engage switch normally located for this car? Is it in the wiper (can't find any switching) or a switch in the gear knob?

What wiring is already present in my non-OD car and what must I add? I found a wiring diagram on the web, but the colors white and yellow with brown or purple tracing are difficult to distingues with dirt and aging (looking at wires near the fuse box in the engine compartment)
Will this gearbox simply drop-in or will I have to make changes somewhere? (I know I will need a longer speedo cable)

Thanks!

Mine is an 80 and the switch is on the shifter.

Advance Auto wire has some great color coded diagrams. Not sure if the factory put the wiring in late model cars that were shipped without overdrive. They didn't in early cars.

http://www.advanceautowire.com/mgb.pdf

On a '79 the switch was in the shift knob. The wiring should be there in the harness that goes down to the transmission (along with the reverse lamp and TCSA wiring).

You'll also need a small wiring harness that is not part of non od cars. It is available from VB for about $15. RAY