Lower=shorter, taller=higher they're used interchangibly. The only ratios I'm aware of in the mk3 were 3.73, 3.91, 4.10, 4.30. I'd never thought about the Landcruiser gears, wonder if they're interchangible.
Whats the reasoning for looking for something taller, mpg, top speed?
I think the point is that 3.73 is short, and that 1st gear does become useless.
With a taller diff, this extends first gear, so that it starts becoming useful again. Or, it could be used to swap in a V160 6 speed transmission with a JZ block.
It extends top speed on the car for those who are gear limited on their top speeds (Not that that is going to happen this side of 500 rwhp, IMO) but mostly, it just gives you back first and second.
The quick way to check for the right (8") ring gear is on the vehicle data tag. The ones that work will be Gxx4 and Gxx5. These are the 8" ring gear with a 4 pinion setup. These ring gears and pinions can be fit into the Supra's diff case, and you'll get the gear ratio that goes with it. If it's a 4 for the last digit, it's a 4 pinion open, and if it's a 5 then it's a 4 pinion limited slip. Obviously the LSD one will be an easier choice, since you won't need to swap in the Supra's LSD section.
Side note for those looking for lower (drag) gears. All Canadian model MA70 NAs came with a 4.300:1 limited slip, so the carrier from one of these will work perfectly, and give you the lower gears.
I used to have a link with what the xx numbers mean in terms of gear ratio, but it's a dead link now.