Long legs are vintage correct for the classic Gibson designs. Short legs were introduced for guitars with shallower pickup cavities (PRS etc...).
Either long or short will be fine in a Les Paul.
That's odd as I had a standard '59 set in an Epi Les Paul and they fit just fine.turns out, i need short legs both neck and bridge. i picked up a set of 59s and they wont fit.
what year was yours? mine is a 2012 custom pro. the cavity isn't that deep and the wires from the switch run directly underneath the left leg and the leg sits right on top of them, forcing the pickup upwards. the stock "probuckers" both have short legs. now i gotta find some 59s with short legs.