After 6 trips to the Eugene, Oregon DMV I finally got all the puzzle pieces together in the proper way and left today with a plate, registration and a title in the mail.
I did the Idaho bill of sale. It took a bill of sale from idaho
an Idaho motorcycle riders manual with the pertinent info highlighted: Page 7
a printout of the Idaho DMV flowchart showing that mopeds are not titled.
An Oregon declaration of ownership form and a fair amount of patience. I showed the clerk in three places where the state of Idaho does not require registration on sub 49cc bikes, they talked to the manager, The manager made them look in a 6 inch thick law book for idaho that neglected to mention mopeds at all, I pointed out the highlighted sections of the Idaho motorcycle manual long enough that another clerk called the Salem DMV who called Idaho and then the clerk looked at me and asked. "Less than 49cc?" I replied yes. "Limited to 35mph?" I said yes and he turned around and grabbed a plate off the shelf.
Result! Fully legal.