It may not be the original body either, may be a Kingswood body. What do you mean by not a commercial? All vans and utes are commercials. N just means Kingswood, M means base model (Belmont in HQ but really nothing, just ute or van. I can them Holden for want of a better term).

XU4 is just a ute or van with passenger tyres hence the lower GVW.