the yj spedo has sensor thats gear driven in the t-case.
that's correct, but it has a signal output (3 wires, ground, +5v or +8v can't remember exactly and signal), the 241OR has the same output but the impulses/mile is different than the YJ signal, you can use a dakota digital box that can be adjusted to correct the signal output. I'd say that's the least of your worries.
roughly this is what you would need for the swap if you plan to do NV3550 & 241OR:
Dodge Dakota 4 cyl trans bellhousing
in case you have an interrnal slave you also need clutch fork, throwout bearing, external slave and hydraulic line
longer slave pushrod (i think it's about 1/2'' difference)
Camaro 4cyl / 4spd clutch disc
Advance Adapters pilot bushing for NV3500
custom rear driveshaft (i'm not sure about the front)
Dakota Digital signal converter box
some work on the t-case shifter