So if I follow correctly the rear drums have been removed and the shoes inspected. Good going! Don't stop there. It sounds like one shoe isn't moving (no brake dust).
One can buy 1-3/8" cups (at least one could several years ago when I bought my spares) and overhaul the wheel cylinders. You should also be able to still get kits that include new piston-return springs. Complete wheel cylinders were over $80/each last time I looked. I have run into aluminum pistons stuck in the bores from electrolysis. They will stick after a few months of sitting in a rainy environment. You can get them out by screwing a zerk fitting in the inlet and hand pumping the grease gun. You can also use shop air but risk shooting the piston across the shop. In any case, with the cylinder bare and clean take your handy dandy wheel-cylinder hone and smooth up the bores, ditto the pistons; then on reassembly coat the aluminum pistons with anti-sieze compound like you'd use for sparkplugs in an aluminum head. Avoid getting it on the cups. That cures the stuck piston problem permanently or at least for years and years. Use the same anti-sieze on the other fittings too, especially the bleed nipples; you can save yourself or someone down the line a lot of trouble. I'm presently setting up to drill one out of an expensive motorcycle caliper.
I have also run into flexible brake hoses plugged with crud to the point that the brakes won't release. There are only three of these on these trucks and they aren't expensive but be aware the NAPA part number listed for the rear axle is about an inch too short. The fronts are OK.
I agree with replacing all the steel lines. A tube bender is a necessity as is tube cutter and reverse flare tool. If you can buy all the lines for your particular truck, great but the tools give you flexibility. Some people like stainless but it's more expensive.
The brake push-rod length is important. If it's too short you won't get full pedal even with the brakes adjusted right up. If it's too long, when the pedal is released the master cylinder cup won't uncover the tiny, tiny relief port in the floor of the resevoir and the brakes won't release. This adjustment is easiest on the bench. Not all push-rods are adjustable. Mine is. This tiny relief hole is also subject to plugging up. Same symptom as the push-rod adjustment being too long. To fix: pull a hair out of your wire brush and with a pair of suitable pliers poke the crud out of the hole. Even your smallest drill bit is too big. Attention to detail is important. Keep plugging away.
