[40 Deluxe]

Sounds like fun! Some suggestions: Take the northern route. Anywhere below 5,000 ft. elevation in Texas, New Mexico, Arizona and California is brutally hot in the summer-110 deg. and up. The 4 speed idea is a good one if you are doing the dirt road bike trail. You can install a 4 speed trans using all Model A parts as this was either a dealer or factory option when A's were new and the parts are still available.
If you break down, one possible source of parts would be to find an older parts store and ask around. They will know all the repair shops in the area, they may have Model A owners as customers and may know of local clubs.
Dirt roads often have severe wash boards which will shake your car to pieces. Keep an eye out for loose bolts and body cracks. Modern suspensions with rubber bushings last a lot longer on these roads. M0odel A's with all metal bushings and kingpins quickly pound the grease out and go metal-to-metal, so grease the fittings every day when running washboard roads.
A rusty body is OK but get the mechanicals in top shape before you leave home! Why start out with worn out brushes and bushings in the starter or generator? Why develop a rod knock or lose a main bearing because you didn't check bearing clearances at home? What is the general condition of the engine? Is the cooling system clean? Is the wiring in good shape, no frayed insulation? You need good lights including turn signals and brake lights (two) to give the all squids on the road a chance to see and avoid you. Model A's are rugged and dependable but need regular care and maintenance.
Maybe someone in a club or on the fordbarn would be willing to be a sort of parts depot for you-someone maybe halfway on your journey where you could stash a couple tires and tubes, tune-up parts, a water pump, etc. and have them ship to you if you break down, thus saving the hassle locating simple items.
Finally, what shape is that old fan blade in??