I would say that for a two inch lift, the diff drop is optional, there are quite a few folks out there running two inch spacer lifts with no diff drop. What the brackets do is "rotate" the front diff downwards, around the nose which stays in the same position.
I would also say that what you have may not be a two inch lift kit, as the two inch kits don't come with the strut spacers that you describe, or a center bracket for the front diff, just the two outer ones, and if I'm correct on that, you're also missing several other bits & pieces - if you go to the Calmini website and look at the suspension systems, you should be able to figure out what you have and what you're missing.
Now - as I recall it - the Calmini two inch kit originally came with four springs, and not just the two rear springs as currently shown, which suggests to me that the lift in front is now being done by building a spacer into the control arm, and if you look closely at the arms in the two inch & three inch kits, you will see that the spring seats are different, so you need to figure out which arms you have, which shouldn't be too difficult, if you need help, take a picture & post it.
The Calmini arms are considered the best part of the kit, so definitely hang on to those, and if they are the newer arms with the built in spacers, fit them with stock springs & struts in front, and the Calmini rear springs in back, put the rest of the pieces on the shelf for now, you will need longer shocks, try Low Range Off Road for these or let me know and I'll see if I can find my notes on the "off the shelf shocks" that people say work with the spacer lifts,