Lowering blocks are fine, good grief. Anything 1” or less isn’t going to change anything you’re going to notice other than the ride height. Maybe if your pinion angle was barely adequate it would push you to needing a shim, but if it was good to start a 1” block wouldn’t put you out of range.
They should have a hole and a pin to locate the block and the axle just like the perch and spring do. Obviously the taller the block is the more you’re going to alter your geometry.
Ford F-250’s 4x4’s from ‘67-72 were called “high-boys” because they had 4” lift blocks in the rear straight from the factory. 4” and even 6” blocks are common for lifted trucks. I’m not saying I’d run a 4” block on my Duster or that it wouldn’t create geometry issues that would need to be dealt with, but a small block isn’t going to hurt anything as long as you have enough tire clearance.