In the "Detroit Diesel Engine Requirements - Lubricating Oil, Fuel, and Filters"
http://www.detroitdiesel.com/pdf/voc...quirements.pdf , they recommend Biobor JF or equivalent. Not sure what brand Newell uses but I would think any brand that you find at a major truck stop would be satisfactory.
You may want to open the fuel tank petcocks and drain the worst of the fuel out (into a suitable container of course).
As usual, Richard is right on about the fuel filters. If you have a bad case of bio-growth inside the tank, you will plug up fuel filters like crazy, time and time again.