Putting drop blocks in the rear, and re-indexing/loosening the torsion bars are the easiest way to lower your truck, but you will loose ride quality, the lower you go, the worse it gets unless you go to extreme measures.
I don't know where you are located, but putting Datsun/Nissan 4X4 leafs in the rear will give you a one and a half inch drop without sacrificing your ride, it will allow you to use a smaller sized drop block which helps with the rear lower shock mount clearance, and they will have a slightly firmer ride, which is what you want when lowering these trucks.
The front is a lot harder to go real low without fabricating/modifying things, it's hard to explain without typing a monster reply, I have a 1966 520 that has had the s*** modified out of it, I have done everything necessary to keep my ride, have it real low, and not bottom out every time I hit a bump or go into a driveway, but it took time to do, to give you an idea of what I have done, I put a flat carrier cross member in(doesn't hang down), I re-located the front rear leaf mounts, I used roadster rear leaf mounts, I used 510 wagon shock mount/leaf mount plates, I have 3 inch lowering blocks, I notched the rear frame 4 inches, I made front drop arms, I re-located the front tension rods to the rear and cut all that mount hardware off the front, I had to route the exhaust system above the cross members, this is only the things I can remember right now, it was less than 2 1/2 inches off the ground till I raised it a little, I hated dragging it to get in my driveway.
Everything has drawbacks, even stock has a drawback, it doesn't look as good as a lowered 520, that's a drawback, you have to decide how low you want to go and if it will be legal, I went to great lengths to be safe, I can take all the tires off the rims and mount the rims, set the truck on level ground and nothing will hit the ground.
I have modified the s*** out of this truck, and it is still not done.
This is sitting on a 1986 Nissan 720 kingcab frame.