Speed Sensor Zf6 swap into ford e350

I just recently finished my 4x4 zf6 conversion on my e350 van. sterling 10.5 in the rear. I know the trucks have their speed sensors in the rear and since I put the zf6 in, I don't really know what to do to get my speedometer working... Also, any ideas for a tach? Any help would be greatly appreciated. Thanks
Need to post more info if you want more than just guesses...

What year is the van?
What year is the Sterling you put in?
Aftermarket tach or factory?
For the tach, I'd take a look at Speedhut.com.

I did a set of custom gauges for my Cummins van and they were awesome to work with. Had some issues with one of the gauges and their customer service was incredible. I ended up with a tach that can run off of any of the sensors for crank or cam position or the alternator signal wire. Programmable and simple to use, plus you can custom design the gauge face.

Does that year of Sterling have the sensor on the diff housing (tone ring on the ring gear)? you may need that to keep the ABS working.

Here's the long and short of it... The 4R100 in a van has an Output Speed Sensor in the tailhousing that produces 3 pulses per revolution of the output shaft. What does the new trans have? Any OSS on the tailhousing? What is the tooth count on the tone ring? If there is one, you need to make it output correctly...maybe with a Electronic Ratio Adapter. If there is no OSS, you're going to have to make one that produces the right pulse count. OR...get yourself a GPS speedo pulse generator.

Those are your options... Go forth and conquer my friend!
The Sterling 10.25 and 10.5 have a VSS tone ring opposite the ring gear on the differential until 2010. In 2011 it disappeared in favour of a VSS in each hub. I can't tell you how many pulses per revolution it puts out.