I cannot really help you but I do want to caution you about using an AR15 bolt release/catch on the LR-308. I built all 4 of mine using the then DPMS approved of AR-15 bolt catch/release only to have DPMS come out last year, maybe late 2010, and say that the AR-15 piece will not work as well as they first thought. Seems some people have had problems with them not locking back and such. So, DPMS now sells a special LR-308 bolt catch and release. I corresponded with DPMS not really wanting to believe that I needed to change out all 4 of the ones I had which I have never had that first problem with, but they convinced me that for $12 or so it would be cheap insurance, so I changed them. No problem on the three DPMS lowers but on the Tactical Machine lower, it was a real PITA to change out, but that is another story for another day.
The new catch paddles are not any bigger than the AR-15 so I doubt the new bolt catch/release would be any better for you, but do make sure you are getting one designed for the LR-308 and not the AR-15.