On the brake swap, you would want to consider swapping out to a later front axle. The disk conversion kits for the 1/2 tons are for 2wd trucks, and then the guys that don't use kits are using spindles from later model trucks, which includes the 3/4 tons, too. In the case of the 4x4, the drum brake 4x4 axle is a closed knuckle Spicer 44, which is a kingpin design. The disk brake spindles from the later 4x4s are an open knuckle balljoint design, and do not interchange. As far as the rear axle goes, you can swap out the 3rd member to change the ratio, just like the 2wd trucks can. Gear ratios are pretty much limited to 4.10, 4.56, and 5.14. The 4.10 ration was used in the '68-'72, usually with 350 and automatic, and it was also common with the Camper Special package. If you want a higher ratio, you'll need to swpa the rear axle. Might be best to swap the front and rear at the seame time to have a matched set. Use cautin with 3/4 tons from the '80s, as many of them used the semi-floating rear axle. that design is not as strong as the full floating axle, which would be the suggested axle for a 4x4. You may consider looking at the '77-'86 K30 and '87-'91 V30 for axles. They used the full float 14 bolt in the rar, and the open knuckle kingpin style Dana 60 in the front. Virtually bulletproof axles for 4x4 use.
