Just saw your post. I need to swing over to Ethridge in a couple weeks and pick up a load of cedar from one of the sawmills around there. Wife wants a "SheShed" with cedar siding.
As a long time bus driver I will say good idea on the RE DT466 and 3060. Really though don't worry about a DT466E or mechanical. It's going to be extremely difficult or impossible to find a mechanical one with the 3060 because of age. Anything past the mid '90s is going to be an E. The only practical difference between the mechanical and E is that the engine warning light on the E will stay on all the time.
Even right after my engine was rebuilt with a reputable mechanic the computer always shows a faulty sensor even when it was replaced.
As far as manuverability: there's not much practical difference between an FE and RE. Yes, the RE has a longer wheelbase but it will drive the one lane mountain roads just as well. Just pull out a little further in the weeds. I will take an RE or FE over a conventional any day, any road. And in dicey weather conditions the RE wins.
Pulling a mountain grade: Any school bus is going to slow down, but a 466/3060 will do as well as any of them other than maybe a Crown. Going up the Cumberland Plateau I slow down to 45 but part of that is going around the curves.