Typically if the speedometer is inop, the odometer won't either, the odometer recieves it's "info" to advance from the speedometer input. The large round electrical connector i believe is for the neutral/safety switch. There should also be the vacuum hose for the modulator. The speedo cable should have the inner cable inside that engages into the square hole in drive gear in the tailshaft. I can't imagine why you didn't see it when you installed the cable, it had to be there on the way to the shop if the speedo worked. I guess I would start by taking the speedo cable off the transmission and examine the inside of the cable end for the inner piece. I don't think the inner part can fall out, I would hope someone would have noticed it on the floor if it did. It's pretty hard to screw this up, worst case scenario is you need a new speedometer cable.
Gilly