speedo gear reduction box part

[75chev4x4]

On my 75 k20 the speedo has never worked. I bought a new cable last week and hooked it to the gauge and spun the cable to confirm that it worked. The gauge is fine but when I get back to the gear reduction box it has a female type end with a spot for a tang and the cable is just a square end. I took the reduction box off the transfer case and it has this male tang thing on the gear shaft that goes into the other end of the reduction box. The gear looks fine so no problem there. I guess there must be some kinda tang piece that slides over the end of the speedo cable that goes into the reduction box? Anyone know what I'm talking about haha? Or where I can get this piece. Love this site btw so much good info on here and nice people. Thanks!