RebelLT, Welcome to the forum.
Handlebar width can be determined by measuring the distance between the boney protusions on the shoulders; just a guideline, of course. Depending on how one fits the mountain bike and which style of drop bar is used, the stem will often be shorter with drops than with flats and drop bar touring bike conversions of mountain bikes often use bar end shifters.
You can see some conversions in the touring forum for ideas.
Brad