Trouble with speedometer cable in 67 Barracuda

I recently bought a Cope Racing Transmission 727 for small block to put in my 67 Barracuda. Now I need a speedo cable for it. I BOUGHT one from Mancini Racing but it's for a 68 and will not work. I TOLD them what I wanted and they still sent one for a 68. My old cable screws on at gauge and the new one pushes on. I just found out last night so I haven't had time to contact either cope or mancini cause of it being sunday, I just thought I get some input.......If my caps are of its because I'm on an I m pad and I'll be dammed if I go back and correct everything on this SOB. LOL