I'm pretty sure that old 66 still runs through eastern OK, sort of alongside I 44.
It's sort of hit and miss from MO state line down to Tulsa, then meanders down to OK City and after that, it's covered by I 40 until you get to Seligman, AZ. Don't drive past the Hackberry, AZ store. It's the only piece left of the town, but interesting.
Don't drive the old highway from Kingman to Needles. Too narrow and rough and twisty for trailers or MHs.
Between Needles and Barstow is some more of it, in small portions off the Interstate.