it would be alot easier to find a 73-87 4wd frame to set your body on than to convert yours to a 4x4 (or so i'm told).
www.lmctruck.com has a good catalog (has alot of drawings on the parts & how they go on).
as far as websites go your on the best one other than this one
www.chevytalk.com has alot of info on 73-87 trucks.buckshot