you can go off the vin of the truck if its original i know one of the digits will tell you, also you can check the casting number on the drivers side top of block where it meets the tranny. then check here http://www.mortec.com/castnum.htm
early 80's shortbed truck with stepside. supposed to have a 350 rebuilt motor and a manual tranny. can't beat 500 bucks on a stepside chevy truck. it is dirty and not a showtruck but it is not too bad. it has dual exhaust with big bells exiting before the rear wheels