If you get down here I can help a bit, or even a beer and a camp night.
You can pick your routes and destinations, and when roads are flat and straight, one road is as good as the next.
From Yellowstone you're just going to be riding home, the only thing you need to decide is where do you want to cross the Mississippi.
Straight east then down the Missouri to StL would be OK by anybody as would coming across on the southern Route 66 thru Tulsa & Joplin, or even some catty-corner way across the plains. But, 66 from Tulsa to StL exists just to mark the southern edge of the Great Plains so that folk avoid falling into the Ozark Mountains.
The bottom 50-100 miles of MO down to Little Rock is IT. Tons of good to great roads, cross the Mississippi at or between Cape Girardeau and Memphis.
I'd put Joplin, MO as a for-sure spot on your map.