I built blanks to go into selected window openings, and that was a bit of work. Removing the rub rails below the windows scared me off the exterior skin option.
Overall, I would think that removing the rivets and doing an exterior skin would be best. It's not that hard to drill out a rivet, and you only got to do several hundred.
Plan your widows and cut the pillars, frame, then skin.
Someone on this site cut their eyebrows off with a plasma torch a few years ago.