i did that route in march, and as last post mentions 1st miles were some kind of surface!- just very bumpy, after that no. probs to Tikal.
Went then to Flores, Coban, Guatemala city, Atitlan. don´t know no. of road, but on my map secondary route (fine red line) from Flores - la libertad - sayaxche there was a small river crossing around here with a ferry, road was fine
(i only got bit unstuck on a dirt road off to the west to lago lachua ) After Coban stuck to main roads (ie yellow and thick red on map) and was good all the way to Atitlan, great views approaching Atitlan