For many years, most major mechanical components of automobiles have carried date and manufacturing codes stamped on them somewhere. Since at least 1955, GM has stamped engines, transmissions, axles, and other components with alphanumeric codes that indicate the date of manufacture, the plant, and even the time of day. Engines would be stamped as to whether it was matched to a standard or auto trans, and the trans would be stamped the other way. If you're gonna pay big bucks for a car, these things all gotta match.
Books are available to break the codes.
These are now typed on a sticker in the glove box, and will be a big help to restorers 30 years from now. As a small manufacturer, it also was willing to build a car to special order with non-standard components. Good luck and let us know what you're interested in.