Saw a K series Kohler on Facebook marketplace listing in Monticello, KY (southern KY, near TN).
Seller listed it as a K121, which of course I had never heard of, so I questioned him about it via the messaging system.
* If you want to see it for yourself, PM me and I send you the link, if you can't find it.
Seller said his son claims it was built one year for concrete finishing machines, electric start only.
Another source I found said it was made for the G. H. Tennant Company only.
Has dual exhaust ports and is equipped with a little electric starter.
Seller believes it to be 6 hp, and says doesn't have a bottom pan and has back plate like Briggs or Tecumseh.
Also has original gas tank, breather, and it runs.
I'm still researching but I did find a couple of things about this motor, although official Kohler info seem to be non-existent.
I know after searching here at Red Square, @hcminis messed with one of the motors a few years back, and I urge him to jump into this discussion.
Also anyone else who might have even the smallest bit of info, please add your two cents worth.
Seems to be as rare as hens teeth or rocking horse turds.
https://gardentractortalk.com/forums/topic/21085-k-121-kohler/