As FarminCy said - bigger OL are already being added.
2014 4 OL: 6'4" 325 lbs, 6'6" 315 lbs, 6'4" 275 lbs, & JC player 6'6" 350 lbs
so far for 2015: 6'5" 270 lbs, 6'5" 295 lbs, & 6'7" 305 lbs
Most are much closer or surpass 300 lbs than in the past.
Strength & Conditioning is another matter. Let's look at the 2 FCS schools that have beaten us over the past few seasons: UNI & North Dakota State. There is a link in coaching, as the new HC for NDSU this year was a UNI-alum if I remember correctly. However there may be a more important link. UNI's S&C Coach is Jed Smith - been part of the program since 2005 I believe. Up until 2002, UNI had Jim Kramer (who left to go the US Olympic Training Center in Colorado Springs. Jim Kramer went to NDSU in 2003 & has been there ever since. This is far from coincidental.
It is more difficult to get sub-250 lb guys up to or surpassing 300 lbs consistently. Plus, someone may be able to make those gains but can they do so & not sustain injuries. Someone who is naturally around 300 lbs may have an advantage to change how their body weight is composed, but it would seem to me their bodies could handle the weight more naturally? That's just my initial thought with no science or anything to back up.
Recruiting classes show we are adding larger-framed athletes to our program. So far for the 2015 class, we have 2 5'11" recruits (1 RB & 1 DB), then the rest are 6'0" or larger regardless of position. Numbers show our team has become 'stronger' - but are they becoming stronger properly to apply to football. Those that have went on to the NFL seem to believe the S&C is very good. They have said as much & some have come back to train. That would leave me to believe we need OL who are naturally bigger & stronger from the get go.