Possible. If it is a '66 casting and there is no VIN stamped on the top rear, then I would think had the engine been in a car it would had to have been either a '66 or '67. If so the pan rail should have the build date stamped on it. When the OP said there were no numbers "anywhere" I took this to mean the pain rail was not stamped also. But that is an assumption on my part.