The speedometer cable plugs into the sppedometer drive on your front hub, and there should be a machine screw that then holds it in place. You should see the small (4mm?) hole in the hub where the screw goes, and if you look at the bottom end of the cable, you'll see a recess in the cable end where the screw shaft holds it in place.
I don't remember how the tach cable attaches. If memory serves, it works the same way, but I may be mixing up my memory between the 350 and 450. My 450 is across town, or I'd pop outside to check for you.