Tried to look it up for you in the BNSF Locomotive Directory 2011-2012, but can't find engine 1320.
Probably no help, but FWIW,
1300 to 1308 are listed as NRE 3GS21C - 9 units
1309 & 1310 are listed as NRE 3GS21C-DE - 2 units
That's all the 1300 series listed, the book then goes to the 1500 series numbers.
Edit: Looks like Martin H got it while I was looking for it in my book, musta been done after book was published?