The W58/Supra is the only W-series box with a 0.78 5th gear. All others are ~0.85.
Simplest way to differentiate is to rotate the input shaft with 5th gear selected.
Put a mark on the output shaft to allow easy counting. To turn the input, use a clutch disc that has a "counting" mark on it or a set of locking pliers (and something soft to protect shaft) on pilot section of input.
Rotate input, counting the turns as you go, while someone counts 10 rotations of the output shaft. This should take a little over 7-3/4 turns of the input for the W58/Supra box. If it takes ~8-1/2 turns it is not a W58/Supra box. The reason for recommending 10 turns of output is that it is easier to differentiate between 7-3/4 and 8-1/2 than between 0.78 and 0.85 turns at the input shaft.
There are differences in the 1st gear ratios of the non-W58/Supra boxes, so performing a similar test should allow differentiating between the various non-W58/Supra options.