Unless Ford has changed things, you don't have any choice of a rear gear.
If you get an F350 Dually Crew Cab Diesel you get 3:73.
If you get an F350 Crew Cab Diesel with Single Rear Wheels you Get 3:55
If you get the F450 Crew Cab Diesel, You will get the 4:30 gears.
Check with your dealer and read your brochure.
When I ordered by F350 Crew Cab Dually FX4 Diesel. I received the 3:73 gears, which is what I would have ordered any way. I was thinking of the 4:10 set, but that is not offered at all.
Like I say, check with the dealer, things may have changed since last October.
Another thing you don't have an option on is the limited slip rear axle.
It's only available on the F350 Dually/F450.
The rest are Electronic-locking.
The following rating are taken from my brochure from last year.
Everything I'm listing are Diesels.
If you go with F350 Crew 4x4 with SRW you have a tow rating of 15,800#
If you go with an F350 Crew 4x2 with SRW you have a tow rating of 16,000#
If you go with an F350 Crew 4X4 with Duals you have 20,300#
If you go with an F350 Crew 4x2 with Duals you have a 20,800# rating.
Make sure of your trailer rating before you buy your truck.
Like I said earlier, I have the F350 FX4 Crew Diesel Dually, and I'm more than happy.
I love this truck, it pulls like a locomotive.
Hockster