Can mast be left standing

>what would you recommend I use to cut the wires (largest is 3/8" diam) to length (grinder cut-off, dremel, or wirecutters?).

A large set of cable cutters is ideal if you can get your hands on them but even a hacksaw will work acceptably. After you cut the cable take a file to the ends of the individual wires and clean them up a bit. You don't want to run the risk of a burr causing your hi-mod terminal to gall.