Michael, I think the best source on Second Manassas is John J. Hennessy's "Return to Bull Run" (Simon & Schuster, 1993). On pages 340-345 he gives a pretty detailed account of Stafford's brigade on the afternoon of August 30 and has a map that shows Brown's brigade stationed on its left and Johnson's brigade on his right. It also shows Brockenbrough's brigade of Lawton's division moving up behind Stafford and Johnston to support them.