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No offense but the lowering blocks are kinda generic and you don't have adequate clearance between the frame rail and the top of the axle tube.

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None taken
I speak from experience when I say the axle-tube isn't the problem when lowering it this way (is there any other way without going to an independent rearsuspension?).
The main problem is the rear axle snubber which is in very close to full contact with the body. This causes you to feel almost every bump in the road.

If you remove the snubber, then the driveshaft will hit the body when accelerating or on good bumps.
The axle tubes only hit the framerail rubbers when cornering hard.

To do a 'good' lowering, the driveshaft tunnel's sheetmetal should be cut open and made higher with a fillerplate.

Stiffer leafsprings are usually a great help aswell after a car has been lowered.
I still plan on adding a couple of leafs on the '57 'cause it bottoms out to easily to my taste.