Route 66 no longer exists - certainly not the route 66 of song and fame.
As a touring option, it is one of the poorer choices since much of the original Route 66 has been overlain with interstate highways. Thus, you are obliged either to make long detours or to ride on the interstate. (Which is permissible in western states - - but why?)
There are Route 66 associations in every state that Route 66 passed through - but again, there are only sections, not a through route, in many states. Especially in Texas, New Mexico, and Arizona - you will be riding on I-40 for much of the way. Even when you aren't, you will often be on service roads with 40,000 cars and trucks zooming by every day.
The proprietor of Crazyguyonabike tried to follow Route 66 and found it a total hassle of service roads and dead ends. There are much better alternative that give you a feel for what Route 66 used to be like and are safe and pleasant.