ALBINS LOW RANGE 2.5 FORESTER : 1.58:1
INPUT GEAR = 20
MATING H-GEAR = 22
H-DRIVING GEAR = 16
MAIN DRIVEN GEAR = 23
Note: Always driven divided by driving
Multiply 1st ratio by 2nd
I.E. 22 / 20 = 1.1
23 / 16 = 1.4375
1.1 x 1.4375 = 1.58 : 1
More details here : http://www.scorpionsubaru.com/low.htm
Here come's the hard bit - Ouch:
LR-053 1.58:1 LOW RANGE GEAR SET FORESTER & OUTBACK = $1 595.00
LR-053 1.58:1 LOW RANGE GEAR SET FORESTER & OUTBACK FITTED = $2 200.00
So if you're in to that sort of thing, might be worth sourcing one if they're still available ...

Cheers, Bantum ...