I have a cable tailhousing for an NP241 that I will not being using, I need the 40 tooth reluctor ring tailhousing I have for my LS1 / electric speedo, my T-case just happened to have the cable drive on it when I bought it. PM me if you want it...
And as far as the hall effect sensor goes -- I'm not entirely sure thats the correct style of sensor for your factory electric speedo setup. They used a 40 tooth reluctor ring, which produces voltages from like .5 to 150 some volts depending on how fast the reluctor ring is spinning.
A hall effect sensor makes more of a direct current square wave signal, which would be useful for a cam or crank sensor, but not so much for a speed signal... If you built the proper converter for it, you could use it, but it'd be far easier to just slap a reluctor ring back in there, and use a factory sensor / DRAC setup instead.