I'm guessing this is a 1/2 ton. You can get 2.5" drop spindles from Classic Performance
CPP for $240 that accept original ball joints and tie rods. You'll have to use a disc brake setup using 71-87 calipers, rotors and bearings. If you don't already know, using drop spindles allows you to go lower while keeping original spring travel. If you want to go lower, you can add 1, 2 or 3" drop coils for $95.
Rear drop coils are also $95 and CPP also has lowering blocks for trailing arms.
AirRide makes a bolt-on rear bag kit for these trucks. I bought a kit from CPP for my '65 C20. Haven't installed yet as I'm still working on the front but, it looks really simple to install. For me, the thing I like about the bags is I should still be able to carry a decent size load in the bed by just airing 'em up a bit to compensate.
-David
