a couple questions for my c- ?? project GMC^2

[84rzv500r]

Amazing amount of knowledge here... spent a few hours searching but need some help...

A jimmy with a jimmy 8...

1) has anyone used a set of Milemarker 11166 lockouts on a Napco 2.5 ton front axle? I need to pull the stub axle flange off to check the axle dia (1.75") and splines (34) but at 5.080" bolt circle it matches up superficially. The napco shop manual is a little light on the big axles.

2) what year did the big chevy's convert to a hydraulic over dual line brake system? It seems a little vague to me.

3) did any years use a hydraulic slave cylinder on the clutch? I am really tight on room in the foot well for mechanical linkages. I have a good single MC that I am gonna use as a clutch master if I can work out a mounting and a linkage.

4) this truck is door tag rated at 24,000 GVWR with 7000 front and 17,000 rear but it has optional 9000 lb front springs and 34,000 lb heavy frame/rear spring (no helpers though) according to the build sheet in the glove box. What do I call it? I think it is a C-55 as I have a C-50 Chevy and a C-65 to compare it to for parts...