The front cross member allows for that front spacer to drop the LCA down while trying to keep the contact minimal. Removing the back block for a smaller wouldn't be a problem at all, and maybe you could compensate in the front with a smaller spacer from PRG...but you're not going to keep the lift you originally had. As far as the driveshaft goes, any lift over 4" in the back (if I recall correctly) recommends a driveshaft spacer for 4WD or a CBDB for 2WD.
Depending on what height you want, you may want to consider pulling the whole lift off and sell then with the funds pick up a mini lift.
Depending on what height you want, you may want to consider pulling the whole lift off and sell then with the funds pick up a mini lift.