You can swap in front disks by simply swapping the steering knuckles, balljoints, and tie rods from a '73-'87 C20.
While true that there isn't anything in the line of gears for the Eaton rear, there are plenty of later model 8 lug rears with gearing as high as 3.55. Depending on what you want to do with the truck as to what diff you would want to look for. If you're not looking to use the truck for any serious hauling, there's lots of 8 lug semi-floaters, mostly Dana 60s and 9.5" 14 bolts, out there. In the semi floaers, I've seen 3.55s (Dana, usually Dodge) as well as 3.42 and 3.73 (GM 14 bolt). those will allow you to keep it 8 lug and have the better highway gearing. If you still want the strength and capacity of a full floater, 3.73 is a common gear with the 14 bolt, and I have seen 3.55 in a full floating Dana rear.
