1968 442 transmission

There's a metal tag on the transmission. Usually on the side. To decode the information you'll need a factory shop manual. Part of the VIN should be on the tag as well as the month and year the transmission was built. You can get a shop manual either on Ebay or from Faxon Auto Literature in Riverside, CA. They have a website. One good indication it's original is if the dipstick says "Use Type A automatic transmission fluid". I believe 1968 was the last year GM was using Type A. After that Dexron was being used. Hope that helps! Jim