The differential, any differential has nothing to do with the ring & pinion ratio. The ring gear drives the carrier which holds the diff and attaches it to the axle shafts. The diff neither knows nor cares how many revs the driveshaft is making.

You're correct that a torsen is the only type of LS which can be used safely on the front end of a pavement driven 4X4, but once you take it off road, you may find it is less satisfactory than you had hoped. A torsen needs SOME load on both wheels to work. If you get a wheel hung in the air, like going rock crawling, the Torsen will act more like an open than an LS. On the other hand when flying low down a fire road or logging trail, the torsen is a thing of beauty and is used on virtually all rallye cars for that reason.

 

For 389.95 from Reider Racing in Michigan, you can get a Torsen 8.8" diff for the front wheels (it's got a special form of limited slip).

The explanation of its internals is at http://www.torsen.com/T2.htm

My question is, how can these diffs operate at any ratio?

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Model: '99 F150 Lariat Supercab 4x4 SS Mechs: 5.4L, 3.73 Diff (9.75" LSD Rear, 8.8" Front)
ORP: Skid Plates, LT265/70R17 GY Wrang. AT/S
Group III towing: HD Electrical/Cooling, GVWR 6500# (Extra leaf spring).
Stuff: Step Bars, 4W Disc ABS, K&N filter, 0W-30 Series 2k Amsoil @ 8200 miles
Stock Items That Differ Across F150s: Steel Driveshaft, Oil filter bolted to engine w/ drip guard, 4R70W transmission.