Here's the conversion kit.
https://www.amazon.com/dp/B0BF84D18H/
Same price on the Walters Engineering website.
This looks much easier to install on the 241C or NP208C, than pulling the 4L80E 4wd unit apart, to add VSS.
Would allow you to use any non-electronic or 4wd electronic transmission, without a VSS OUTPUT Speed Sensor to your stand-alone ECU or digital dash.
ALMOST wish I had found this earlier...
Might not have rebuilt my 4L80E, got lazy, installed a used unit with a stand-alone Transmission control. (Not a good idea, because the 92,000 mile refresh is a lot less expensive than the 250,000 mile broken hard parts, to repair.)
Purchased an internal 40 tooth reluctor to install inside my 4L80 when apart. The gear was $39.00.
Adding the rear sensor to the 4wd transmission requires complete overhaul to the rear drum, where it requires being pressed onto the drum, while out.
The Walters Engineering kit is an excellent option, since you only have to remove the transfer case tail shaft cover to swap out the internal parts.
However, not replacing the bearings, seals and shifter fork polymer bits, could come back to haunt you.
Would recommend you look into the NP241C "DT" rebuild kit, clean paint and restore the transfer case, fresh bearings, fork sliders, inspect gears and measure chain wear, while you have it out.
The 241C kits come in 16mm thick input bearing or 24mm thick. Wide is better, if you can run it.
Verify you have room in the case to run the wider bearing, before you buy a kit.
This is the wide bearing kit:
https://www.amazon.com/dp/B07HCSY3ZK/
The "DT" Brand is good, if you can find it. Stay away from ChiCom bearings.
Most offerings on Amazon clearly advertise Japan made bearings.
Borg Warner Chain, if yours is stretched:
https://www.amazon.com/dp/B07987GPWQ/
There's an acceptable distance between the links, when you open up the unit and squeeze the chain together in the center.
If I have the NP241C repair manual, I'll post the measurement for the chain stretch, unless somebody else gets to it first.
Good score.