I have a Clinton Chief J-9 and I am guessing its a mid 60s model. 66-67 by what I can see online. Serial number is 66045. While reading what I can find on this motor I saw that Clinton Engines sold or moved from Clinton Michigan to Maquoketa Iowa in 1950. Any pictures of the ID plate I see on motors similar to mine have Maquoketa on them, but mine reads Clinton Mich, USA.
Seems odd to me that 16 or 17 years later they would still use an old nameplate.