I fish that area numerous times a year. July will probably be VERY hot, so hopefully your two hours is in the morning or evening.
If you are continuing your trip on HWY 5 I'd say Upper Sac in or around Dunsmuir. You can park your car and walk 30 feet or less and start fishing. Be sure to visit the aforementioned Ted Fay fly shop
in Dunsmuir for the very local scoop, maybe buy a few flies they suggest or whatever. They also have an online fishing report
for the Sac and McCloud that is always fun to read.
McCloud is awesome, but with only two hours to spare the conservancy especially, is not an option. McCloud the town is what guys? 12 miles from HWY 5 each way? and the dirt road down to Ah Di Nah/conservancy is 30-45 minutes right? McCloud is technically more east than south of Mt. Shasta town.
The city park in Dunsmuir is popular and recommended frequently to tourists. Try the Scarlett Way bridge and fish upstream from there - if you've got more time go along the RR tracks, fish sweet spots along the way and end up at the waterfalls (Mossbrae Falls - had to edit this in, forgot the name, I must be old!) that is one mile from the bridge.
If you want a really good map of the whole country check out postholer
, with the mytopo option clicked on -a topographical map of the whole country, some areas better than others. It also has all the major hiking trails mapped out. The topos are really good for that area.