Outer Limits 4x4 Board

i am running a commodore 3.8 auto in my 90 lux, and just wondering if any
one knows where to buy the speed sensor part that the speed cable screws
onto on the transfer case. im thinking you have to buy it from marks but not to sure, any help would be much appreciated

MARKS IS THE PLACE ALLRIGHT.

shouldnt the speedo cable screw straight into the transfer and not the auto with the auto you get rid of the extension housing when you put the adaptor on it. the computer only needs to know speed to lock up torque convetor which can be over ridden with a switch which is better for down hill descents