its not a genration thing they are looking for
the parts manual specifies 01, 02, 03 and those being Gas, LPG or Duel Fuel (GAS/LPG), all in that order.
01= Gasoline
02= LPG
03= GAS/LPG (Duel Fuel)
The most common trucks on the market are the LPG trucks and the the packing kit part number for those trucks is 9430430140. Takes 2 kits if your doing both. There may be a sequence change in part numbers and a newer one available but just give them this number and it should suffice. Actually i checked all the packing kits for all types and they are all the same. ;o)
The only time you would run into model type problems is if you needed any hard parts like rod's or packing glands etc. But as for the packing kits they are all the same.
good luck