The last HD dealer in Yankton that I know of was George Martin in the mid 1950s. He was Badly injured on the shoulder of hwy 81 about where Wilson trailer is now. He was working on a cycle when a drunk driver hit him. He was later in Lesterville then Menno. Auctioned his shop in the mid 1980s.
Ryan oil was the Chrysler Dodge dealer. I remember a late 60s Hemi full sized, New Yorker?, in the showroom. Walt Nelson had a shop across the street and 1/2 block west. Later in a old railroad depot.
Zimmerman motors was Plymouth on hwy 50. Bud Rieman had the shop across from there until he went to prison for the rest of his life.
I know of one 1950 panhead that had been chopped and now returned to stock.
One old 45 flathead chop might be in a warehouse yet.
One man I remember from the Scrambler club days, mid 1970s, later had a Honda shadow I worked on, came riding into HyVees parking lot on his old chop a couple of years ago. Panhead, at least +12 forks, 5 ft high twin fishtails. Cloud of smoke from everywhere. I just shook my head and smiled.