qwertypoiu makes a good point, on keeping it stock. While I'm by no means an authority on Pajeros (or any other make for that matter) I think that later model Pajeros come with a hood scoop, for this very purpose.
If your engine feels "choked" or "suffocated", more often that not, it's possibly because of a poorly fitting / dirty / desi-made air cleaner / filter. Another likely culprit can be faulty connections between the air filter onwards. So, instead of rushing out, to make expensive (and often unnecessary) body modifications to your machine, it might make sense to troubleshoot it from the very basics, and then work your way up towards the more complex.
Snorkels, and hood scoops, and other modifications, are a different matter altogether. If your vehicle feels like it's not breathing right, in STOCK condition...it's a more than likely chance that it won't breathe right AFTER an expensive, after-market modification.
As for the questions pertaining diesels, and as to can it be done...could it be beneficial...are there other means to improve engine efficiency...the answer to all of those would be "yes". Theoretically speaking, as well as practically.
Like I was saying, though. It should be perfect while stock. After-market mods just make it slightly perfecter and perfecterer.