The 10-3 wire is now short, can I use a j-box and add to it to make it long enough to reach the new location. The j-box is accessible on the ceiling of the basement.

Of course, that is what a junction box is good for ,extending cables that are too short.

tkrussell, would twist connector work here, or should another type be used? Thanks

Twist connector? Do you mean for the splices?

Sorry, wire nuts for the splice or something else?