The '98 was the odd duck as it was the only Fozzie to get the EJ25D - Phase 1 DOHC - engine. All the '99+ received the Phase 2 SOHC.
If they swapped in a newer model year, then they most likely had to change the wiring, which means you'll need to do more checking to figure it out. I know the DOHC EJ25 used expensive NGKs - I'm not sure if the newer SOHC EJ25 were the same.
The other option is they swapped in a '95-98 EJ22 Phase 1. These are common swaps on Outbacks, etc. w/the EJ25D due to the infamous HG failure, as they are 99% plug-and-play.
Do you have the two vertical bumps in the timing cover on the left and right side like i49.photobucket.com/albums/f280/vintagefortytwo/Forester/Forester%20XT%20Motor/IMG_0526.jpg (one side is missing the cover) or just one like brastic.com/sterling/ej22_stand.jpg ?
The 1st one is the DOHC and should be the same as what came w/the car. Also, if you look on the top of the block under/near the P/S and the Alternator it is stamped w/the engine size.
