Why do the gauntlets say you need to be level 60 to attain? Aren't these crafted? You should be able to get them at any level if you have the pp. I just bought a few pieces today for around 1k - 2k pp.
You can't have a piece refitted once it has been made. But a smith can make you a large version by using a large plate gauntlet mold instead of a medium one.