How many days are you looking to do it in? What kind of daily avg are you looking for? I've done a bit of cycling in Mexico and I just finished putting together a decent little itinerary for Mazatlan to Guantajuato, and then there to Toluca (or could easily end in Mexico City). If you're looking to spend a little bit of time and not push too hard, I've got it as a route with a 73 km/day avg, 18 cycling days, and 4 rest days. I rode from Mazatlan down the coast to Puerto Vallarta, and continuing downwards on the 200 which was ok, but I don't think the best route. I think from Mazatlan over the Espinazo del Diabolo to Durango looks fantastic. Great scenery and an amazing road. Then from Durango you can head down to Zacatecas, Aguascalientes, and Guantajuanto which all have great colonial historic centres.

Crazy guy does have some good resources in other journals, and one other thing you can do is use google street view for many highways in Mexico. Just drag over the little man and it shows which roads are available, that way you can get an idea how wide the highway is, what the traffic levels are like, and even how scenic it is. Feel free to msg me if you want some more details on my little itinerary too - it's terrible weather here right now, so I just keep creating cycling routes that I want to do to distract me! Good luck with the planning, and enjoy the journey!!