as far as shifting the 2-speed rear, I am not an expert (there are guys on here that have been driving them way longer than I but, using your terminology, if you are in low, you activate high, then let off the gas a bit to allow it to shift into high. if shifting from hi to low, activate low, let off the gas a tad, then give it more gas.
I have a viking 60 (1958) and the tag on it says 16,000 pounds. Yours probably has a bit heavier axles and springs to make up the difference. Mine has a steel dump on it and also weighs about 9 empty. I don't shift the rear unless I am real loaded (pulling my 7,000 pound travel trailer) and even then, only if I am going up a hill and need to find the right gear.
As far as bleeding brakes, I made a power bleeder out of a cheap garden sprayer and an extra master cyl cap. Bleeding sequence should be pretty much the same as on my 58 with the hydra-vac. Hydravac unit has 2 bleeders on it, bleed the one farthest away from the output line first, then the one closest to the output line next. The link below is the sequence for the 55, which has the hydrovac unit on passenger side. My 58 is on driver side so, I swapped the order of rear wheels (per instructions in my 58 manual). Pay attention to the loosening of the upper shoes before bleeding! (if you have the same brake shoe setup) otherwise you won't get all the air out.
http://chevy.oldcarmanualproject.com/shop/1955truck2/55ctsm0507.htmAs far as your transmission, it is probably an SM420, and 1st is not synchronized so YES, it will gtind when going into 1st unless you are barely moving or double-clutch it.
