Driver side bank: cylinders are 2,4,6 & 8
Passenger side bank: cylinders are 1,3,5, & 7
(It's opposite of a traditional GM gasoline motor.)
Here's a little advise: Never change only SOME injectors on that year Duramax. Replace them all...as a set only (all 8). There are a couple reasons why. Sometimes you may have high balance rates on one cylinder as a result of another injector issue. Another reason is if one or some injectors are bad, the rest are very soon to follow.
As for the required parts, here is a list including the part #'s.
8 injectors, 97729095
2 rocker cover gaskets, 97188896
8 return line seals, 97228933
2 return pipe seals, 97600925
2 fuel feed hose seals, 97251047
1 water outlet seal, 94011604
sealant for upper rocker covers, 12378521
fuel filer, 12633243
gallon of Dexcool coolant
I hope he knows what he's doing. It's no simple task like screwing in spark plugs. There are a couple critical things along the way that shouldn't be overlooked. Good luck!