Also -- any thoughts on hood louvers? Like these? Anyone had success? Ambient heat on diesels is pretty significant so even if it sucked out a few degrees F it'd be worth the investment.
What I don't understand is how the insulation pad under the hood is dealt with. Mine is a good 2.5" thick or so. I feel like you'd have to cut out quite a large hole to let the louver work properly.
I've got them on my 4.0, having pulled the whole hood from my previous 4.6 Disco that died (cam lobe wear issue/top end lubrication; totally unrelated to louvers).
Soundproofing pad on the hood will have to go to make it effective unless yours is pristine and even then you will be working around how to keep it in place after cutting massive holes in it. It will make the ride a bit louder, or at least it did in my petrol truck(s). All of that is relative of course given the exhaust, or the lack of soundproofing under my carpets right now.
Here's a couple of streetside shots since I haven't taken many this fall for some reason, at least not head on:

Sorry for the iphone quality and lighting, and ignore the half finished solenoid relocation/eventual mesh grill and such-she's a work in progress.
Overall I like them-with the hood blackout they don't stand out that much and the certainly seem to move heat out of underneath the hood (especially when you're not moving or after you shut down). Water ingress is something that people may raise as an issue but I haven't found it to be of any significance (and I have a lot more electronics to worry about than you would with your diesel). Simply put if you wheel anywhere with water your engine gets plenty of exposure that way from underneath, with the louvers pointed backwards facing up hill and raised off the hood the vast, vast majority of water runs right past it all.
Hope that helps give a first hand perspective.
r-
Ray