Need advice on suspension and brake upgrades

Try Speedway Motors, I buy a lot from them, they are pertty reasonably priced. "speedwaymotors.com"
You cheepist option for disc brakes is to pull a set of a '70 or later 'A' body form the bone yard. At least the spindles and possibly upper control arms. Pads, calipers, hoses, rotors and wheel bearings are still available through the local parts house or Rock Auto.
Small bolt pattern though, not sure year they switched to the larger pattern.
Rear brake drums, a tape measure to measure diameter, anything under 10" you have 9" drums, 10" or more you have 10" drums.
They will allow up to 0.060" over size before replacement.
You rear diff. is probably the 7" light duty.