On the 4x4 boxes it was on the N/S/F driveshaft. I didn't realise you had a rear wheel drive one.

The speedo output should be at the back of the box around the output flange to the propshaft. If it's not there then it must be driven off a wheel.....

I know Transits used a cable off the back of the box up until 98 then they used a speed sensor in the same position.