I, and others, have posted a lot of info on Transit drivetrain options on the usafordtransit forum.  Yes the rear diff is a standard Ford Stirling.  Rather than a clutch pack Ford LSD, most would agree the geared TrueTrac LSD is a better choice...I have one F and R in my Quadvan 4x4.   Rear was $1100 installed i think at a local 4WD shop.  I toyed with the idea of an ARB locker but IMO that only makes sense if you’re doing a 4” lift, low roof van build with >32” tires.
	
			
			 
				 
 
		 
 
		 
					
				 
						
					 
	 
	 
 
		 
 
		 
 
		 
 
		
 
					
				 
						
					

 
 
		 
 
		 
	 
	