Looking at this further, Reyes started-off his first 4 games in 2004 (his second year) in Carolina at LG. He got hurt and when he returned, they put him at RG and kept him there for the next 24 games. Now since the Panthers have had a good O-line for years, I'd trust their OL evaluation skills (sorry McNally!) and say that Reyes would be best-served at RG and SHOULD be the starter at RG now. He's got more experience, if not more talent, than Preston, and at the least experience is what you want/need with a rookie like Pennington starting at RT.
At LG, I'd be fine with Merz, again because Gandy is probably gone and proving not to be so great at LG. With the season essentially being over and JP getting the greenlight to move around, now's the time to start experimenting on the O-line.