Isuzu ELF truck which come with 4Hseries of engine first start with engine code of 4HF1, which it have NPR, NKR and NKS model.
The first generation of 4HF1 engine rocker cover design as it have 15 screw holes on it, and than it come to 2nd generation of 4HF1, or may be it is call 4HG1, have the same number of 15 screw holes on the rocker cover but the gasket is design as such it looks thinner than the first generation.
And it come to 3rd generation of 4HG1, the gasket is about the same thickness with the first generation but it only have 8 screw holes.
It is quite confusing after this when the 4HK1 is start to rolling on the road, the rocker cover gasket have an another design with 10 screw holes and all of sudden they design the another type of rocker cover gasket with no screw holes at all.
Beside the rocker cover gasket, you may facing the difference of oil pan gasket, valve seal and oil cooler gasket from the difference generation of Isuzu 4Hseries of engine.