gen 1 (96-99) OB struts allow for taller tires than gen 1 (98-02) FOR struts. The lower spring perch on those FOR struts is a little lower/closer to the hub, allowing for the taller forester spring. BUT if you squeeze gen 1 FOR springs into gen 1 OB struts, you'll gain close to an inch more lift than using OB/Legacy springs in OB struts.
BUT, if you use (98-02) FOR springs in (96-99) OB struts, you need to use the upper spring perch for the forester springs in front, under the top hat. Those FOR spring coils get smaller whereas OB and legacy springs do not.
99 FOR front spring
97 OB front spring
Gen 2 FOR struts are best used as a complete assembly. Best to get some take-offs then they just bolt right up to most imprezas.
When I lifted a 93 IMP on 99 FOR struts, I had to use the IMp rear top hats as the early IMP top hat bolt spacing was smaller than the FOR and OB (later IMPs and WRXs are like the OBs and FORs)