If the Pats could reach a reasonable contract arrangement with McNeal, I'd jump on this in a nano second. Quality LTs are a gift in this league and McNeal is a good one. I'd then move Light to LG, Volmer to RT and have Kaszur backing up all 4 OL positions. A Volmer/McNeil Tackle duo could be a elite pairing for the next 8-10 years, and I believe that Light at LG would be only a marginal downgrade to start with, and by the end of the season, he'd be playing at an all pro level.
I think the Pats have a very rare opportunity to trade for equal value in a player as opposed to draft picks. If trading an elite OG for an elite LT isn't your cup of tea, there are over 200 RFAs. all of whom are pissed at their situations, to choose from.
Mankins is worth a first round pick, but it might be very difficult to get one because everyone is aware of the "disconnect" between Logan and the Pats. Also it would be hard for any team to be willing to give up a first rounder for an interior OLman.
Personally I'm hoping he'll be back, but unfortunately the Branch deal set the precedent for a player being able to shoot his way out of town. That being the case, this is best environment in NFL history to make a player for player trade.