LI means Long Island, where the current Brown company resides .... no help to you
hard to tell anything from that pic, but you [he] appear to have a GM based delivery van commonly bodied by 3rd party specialty companies .... likely be basicly a 3/4 or 1T Chev or GMC chassis delivered to the body maker as a chassis only model [3500 = 3/4T, 3700 = 1T], so the chassis and mechanical would be covered by the 57 shop manual, for the body and interior detail you're on your own if the company has 'disowned' their previous life, but the dash [gauges and controls] might be GMC or Chev
Bill
