You can swap the top end over to an LLY for an 01-02 LB7, and run custom EFILIVE tuning to make LLY sticks work in an LB7. For an 03-04 LB7 it is cheaper to just swap over to an LLY engine as it is plug and play. i believe you can swap LBZ injectors into an LLY, but not LLY's into an LBZ. And LBZ and LMM swap back and forth directly(except LBZ is 7 hole VS the LMM's 6 holes).
If the nozzle wasn't the issue, why did Isuzu switch to a micro-blind type with the LLY? I wouldn't really be concerned about them being smaller, that is easy enough to resolve.