This is from Justin's own website. Forced to choose, I am going to have to side with him on this one --
"Justin is a graduate of Plano East Senior High School (PESH) where he started at left guard for three years. In May 2008, he was inducted into PESH’s Hall of Honor for his accomplishments on and off the field. In May 2013, Justin was inducted into the citywide Plano Independent School District’s Hall of Honor...."
https://justinblalock.com/about-justin/
".... Blalock was born in Dallas, Texas. He attended Plano East Senior High School in the Dallas suburb of Plano. He was three-year starter at offensive guard, but also saw playing time at defensive tackle. As a sophomore in 1999, Blalock was named second-team all-district after recording 151 pancake blocks, as he helped lead Plano East to an 11-3 record and the Texas 5A Division II state quarterfinals that season....."
https://en.wikipedia.org/wiki/Justin_Blalock
" ... A three-year starter at left guard for East, Blalock was a top-rated offensive lineman that signed with the University of Texas. By the time he graduated from UT, he had won a national championship and been nominated for the Lombardi Award and Outland Trophy, awards given to the top lineman in the country. While at UT, he also made the Athletic Director’s Academic Dean’s List twice...."
http://starlocalmedia.com/planocour...cle_a1e9d0b4-21f9-11e6-85dd-a397e8747d11.html
The recruiting services also listed him as an OG
https://247sports.com/Player/Justin-Blalock-26759/high-school-43564