Another vote for EZ66 Guide. I have several sources, find this one the most useful.
Figure out how much time you want to spend. There is a lot to see along the way if you intend to soak up the history. My last run on the western Oklahoma and Texas Panhandle section was four days from El Reno to Tucumcari. It could have been more than a week, if I hadn't bypassed so many potential stops. There are other sections equally interesting, and sections where there are few reasons to stop.
I ususally use the alternative Interstate (55, 44, 40) to get around or through major metro areas, because if there we not stops you wanted to make, you will find the city street routings slow going (if still available, urban expressways greatly changed the streets and landscape).
The route through Tulsa is marked, and has historic restorations and nostalgia businesses along the 11th Sreet routing, but you'll still have to get on I-44 or I-244 to get across the Arkansas River. The route through Joplin isn't bad. But I wouldn't try to follow 66 street routings through St Louis or Oklahoma City.