Hi Gadget
on the 660 the latest maps should have overwritten the old ones. If you still have two sets of maps on 660 Tools, Settings, Map, Map info and then you can untick the one you don't want
In Basecamp you have to click the drop down menu to change maps so you should not pick the wrong one. Even if you do the 660 will calculate the route using the new maps.
I keep several maps on my PC and can switch between, that's how I know that openstreetmap has more accurate mapping around here than Garmin!
John
PS The driveshaft is in the K75 and the bike is up and running