Welcome to the madnees know as Big Bolts.
1. The reply above covers this one really good? You have a higher rearend gear with the two speed, and if driving around empty, you won't need to use low at all.
2. Tire size can vary, it you 20" wheels then it most likely still has the split rims. those are getting harder to find some one willing to change. if it has 22.5" rims it may have one piece replacements. the 22.5 tires are a common size used in bigger trucks, you should have no problem finding them, but you really need to find out what is on the truck first. if you have split rims you may need to buy new rims as well.
3. I guessing all six tires are on the four coners, dual in the rear? yes all six have brakes, but the rear duals share the brakes on the rear axle, so there are only four brakes sets on the truck, well five if you count the park brake.
4. Yep, I have done so in the past when if was all I had to drive, if it's a short wheelbase it not much more than driveing a dually pickup. MY L60 would made a good daily driver as the wheelbase is 121" which is 6" shorter than a long bed pickup of the same year.
I'm sure Burgie will be along shotrly with this link too
http://www.chevyc60.com/ . My truck can be seen here:
1960 Chevrolet L60 Viking LCF .
Enjoy.
