Just wondering if there are any interchangeable parts from other jeeps eg twin(or more) piston calipers, brake booster decent bucket seats height adjustable steering column 3.0 crd from the grand cherokee etc etc??

Generally speaking, any parts that were not engine-specific on the Liberty / Cherokee should bolt right up to the CRD Liberty / Cherokee.

Unfortunately, you will be somewhat on your own to investigate the parts if for some reason the part numbers don't want to match up based on application.