my guess is 4-6% at 200lbs.
based on his pics he was about 4-6% bf. i have heard in his prime he was 202 lbs. i dont know if these stats were concurrent but based off looking at the physiques/weights of other athletes (gsp and matt hughes) that they were.
based of looking through his book on strength, which i dont want to find a link to because its easy to find, his exercise program was split between REALLY low weights at dozens or even hundreds of reps and olympic type lifts and old school strongman lifts at presumably high weight.