Many different ways go get there. My suggestion is shown in the map above.
Scenery
The lake is very pretty there is a very nice over-flow dam that is amazing. most the road has trees next too or limbs hanging out so lots of shade to cool off in.
Drive Enjoyment
The road over all is very good pavement there is some dirt and gravel patches from trucks, not many potholes. And there are loads of good curves and twisties and some 90 degree turns.
Tourism Opportunities
There are designated camping areas and swimming, boating, fishing areas and for meals and gas stops. Okmulgee has it all ... plenty of off-bike options to enjoy.
The roads are dismal for the most part. 56 and the areas immediately by the boat launches are pristine, but that's about it. There's grave roads, and a bridge that's been out both times I've done this ride (2012, and 2017). There's also only amenities at the beginning of the route, fortunately that's all you really need. Even so, the road IS fun. Be prepared for adventure, and make sure you know how to ride loose for when you're in the soft stuff. Sand is ALL OVER on this run. I certainly wouldn't advise trying to do any Valentino Rossi impressions.