Onwenu needs to stay at RG. I'd rather sign two tackles than sign Smith and kick Onwenu out to RT. Jackson played RG early in his career, and would probably be fine with a move to RT. Sign Stanley and Jackson.
More realistically, it's Stanley or Jackson at LT, and Campbell or Ersery at RT. If we're drafting an RT, I think the preference for one with some LT ability is important. Can't go back to anything the team had last year at LT. If something happens to the FA LT, there has to be a new replacement available.
For the record, I'm in the camp that Campbell is going to do just fine at tackle.
Matt Light had sub 34" arms as well.