Well per the manual when towing flat(on all fours), you need to remove BOTH drive lines. At least that is what's in the manual for both my 82 SX/4 and my 86 Limited Wagon. they both have NP129 cases, while one is a disconnect axle(the 82) and one is a solid axle(the 85). I believe that the requirement to remove both shafts when towing flat is universal as none of the Eagles had a Neutral position in the transfer case.
PS the Only towing configuration other than a trailer that is supported without removing a d-shaft is one set up in the air and the other on a set of AUX wheels. I cant even remember the last time I saw a set of those, but I vaguely want to think it was on an old Wrecker/Tow Truck...
Doc