Another good reference source are the Chevrolet Communication kits.These are the monthly boxed kits filled with Booklets and letters,as well as 35mm color filmstrips/records previewing the cars.
They were sent out to the Dealerships to inform the Salesmen whats what.The information,not to mention the color stills & narration are the closest thing you can get to stepping back in time!
I collect all of these,& can dig out a desired model year sometime,to see if there is any mention of the transmission availabilty.