None really, there basic crude and a little less creature comforts compared to the civi models. Some Wolf TUM may be 24v which can mean parts can be expensive but the standard 90,110,tithonius will be 12v and the FFR's have 24v aswell on a separate system but you don't need to worry about that unless you want to use it. most will be 2.5N/A which is slow and underpowered by todays standards but I like it. most transplant a disco 200tdi as it transfers across with very little modification.
the HD chassis is made of a slightly heavier gauge steel but apart from that there standard fitment for defender body parts. The only exception to this might be a snatch chassis which has different mounts for the rear body.