totalloser

It's been a while since I looked, but I think the eth engine actually already has a slightly larger intake elbow. Sits a little taller. Also there was actually an intake "issue" early in the 24 valves that pinched off the flow to the #1 cylinder making it run a tad hotter due to getting slightly less air. I think this manifold was changed to a better balanced design in 99 or 00, but can't remember. I do remember that I determined that mine didn't have the pinched #1 port, so yours probably doesn't either.

Go over 350hp (crank) you'll probably need to think about clutch. Go over 400hp and it's time to thing about a turbo. 400hp and below you'll likely get better performance from the stock turbo if you turn it up. Smaller turbo=quicker spooling.

Having said that, variable displacement and ball bearing turbos tend to bend this rule. There is also one other persuasive reason to keep the stock turbo. Exhaust brake. You can get an exhaust brake right off the tail of the turbo. Most (all?) aftermarket turbos do not support this possibility.

Over 400 hp and you will have to make compromises on the clutch. Either a faster wearing kevlar, or grabby ceramic disc if you want a single disc, or BIG money for a double disc clutch. At 400hp you can use a stock style friction material with a beefed up hub. That's what I'm running.

MANY ways to skin a cat. To get better info, you probably need to narrow down how much power you are shooting for, and there will STILL be many ways to accomplish what you have in mind.

Trboluvr

The stock 6.7 turbo is variable AND has a built-in ex-brake. It is not a direct bolt-on but fairly simple with the 6.7 manifold and fleece controller.
ANY other aftermarket turbo even twins/triples can be used with a downstream inline ex-brake. So thats really not an issue.

vp dually

I know that every little thing helps.I think the power(hp/lbs) that intakes provide is minimal.It may help overall in conjunction with other mods.But in of it self not much.Imho

Trboluvr

In a diesel, fuel makes power. but without enough cool air, fuel cant make as much power.
example: put 250hp injectors and a comp in a VP truck with stock turbo. it may make 400hp. drop a 62 on and it makes 500hp, drop a 475 under that 62 and it makes 600hp.
Now go back and look at the driveability of those trucks and the twinned truck has the most useable power because it has enough air for the fuel.
further air flow enhancements can easily put it over the 700hp mark STILL WITHOUT adding more fuel.
IMO thats why there is such a spread on dyno sheets with guys all using 150hp injectors, from 400-600hp variance.