Be sure to do pre-1937 66 in New Mexico. Most of it is still there (and used), though short sections are now only accessible on foot. And you'll see where 66 crosses itself, too!
Most notable among the places no longer drivable along the pre-37 route is La Bajada Hill between ABQ and Santa Fe. It was quite steep, making it impossible for owners of the (unmodified) Model T to go up the hill moving forwards. They could, however, put it in reverse and back up the hill.
:)
Lynn