If you dont know much of the history in regards to the servicing. I would do a 50,000km service on the old girl.
Im assuming its a NA gen2?
Spark plugs id use BKR6E-11 (they are fine for 50,000kms' which is when you should change them next
Leads... Bosch.. always.
Fuel filter (Z348)
Air filter (A360 im pretty sure then gen2 jiggas are)
3.3ltrs Gearbox oil (75w90)
0.9ltrs Rear diff oil (80w90)
6ltrs Coolant
Brake fluid flush, Dot 4 or 5 will do
4.2ltrs Engine oil, 10w 50 semi synthetic (there is no point using full synthetic in an engine with over 100,000kms)
oil filter (use genuine, i always do with every subaru i service or build) Z459 is the ryco number i think.
upper cylinder spray aswell goes down a treat.
i normally put a set of fan belts on too every 50,000kms, 4pk895 5pk875 ( double check that though)
If your has an air flow metre i would spray that with Electrical contact cleaner aswell or you can buy stuff called (air mass metre cleaner).
tweak up the hande brake and the off you go