Here's the information packet from the GM Heritage Center archive for an '86 Chevy pickup:
http://www.gmheritagecenter.com/docs...olet-Truck.pdf
I'm not seeing an overdrive automatic in the one tons, so someone may have stuck that in there, but everything else seems to be available.
As Bob suggests probably easiest to look at the SPID label (service label) in the glovebox if it's still there.
Lastly, if you are really desperate, you can send the VIN and $50 to the GM Heritage Center and they will send you the actual invoice (RPOs and pricing) for that specific truck.
http://www.gmmediaarchive.com/
K