They're probably going to do something about that picture. Here's a link to a handy thing I discovered for posting things here. I bookmarked it.
https://dl.dropboxusercontent.com/u/201045551/Forums/PhotoUpload/RV.NET-Photo-Upload.html
With the five diesel trucks that I've owned, I would say that I never experienced anything with stock gearing that made me think that something bad would happen to the drivetrain. Your modification list is very mild and I wouldn't worry about it. You are already dealing with parts that were engineered for heavier duty use than what you've described you'll use the truck for.
But, I can understand why a couple of the manufacturers have offered lower gearing. I'm not saying it would be a terrible idea, but it will affect drivability. Your best bet may be to do a google search on the rpm that the truck should be cruising at. You'll find answers quick. As far as I've ever heard, anything lower than 2000 is a golden area for mileage. As far as what's best for cruising with a heavy load on or attached, the latest information that I can give you is that the 1997 dodge that I mentioned cruises at about 2200 at 70mph on the highway. When a grade comes, I push my foot down and the truck goes and there is plenty of pedal left. No need to downshift or anything.
You'll have to experience the truck with a load on. It's unbelievable how more weight won't affect your power.
4.10 gears wouldn't be a bad idea at all. All I'm saying is I wouldn't think it necessary.
Do you know anyone with 35" tires with a newer ford bolt pattern that would let you bolt them on for an hour or two? That would give you the best idea of what I'm saying for now. They may rub a bit with no lift in the front, but they should still bolt up and clear I believe. Somebody is welcome to comment and let me know if I'm wrong. I believe my 1999 had just a leveling kit and there was plenty of room.