My favorite "Long" day ride is Spearfish to Buffalo via US 14/16, then over to Ten Sleep, up to Greybull, Up Shell Canyon to Burgess Junction, Over to Ranchester on 14, Gillette via 14 - 14/16. Slab it home from Gillette.
It is a shade over 600 miles and can be done all in the daylight from May - September if one doesn't dawdle.
May or November, I can't remember.
Looking at your map, where is the Spearfish to Buffalo 14/16 section? This looks so neat, we may slab it from CA, just to see some stuff East of Yellowstone!