I have a 98 legacy gt 2.5 dohc and a 04 forester with a sohc
No can do !
That is a strange idea. Lots and lots of work for no apparent benefit.
Well, the benefit IS that if the head gaskets on the newer 2.5 sohc are new it's a FAR more durable motor than the fragile earlier DOHC from the late 90's. But, yes: lots of work as the exhaust, ECM, harnesses have to swap over. Seriously: throw the '98 DOHC away!
Looking for a Used Subaru in your area?
CarGurus has 128,984 nationwide Subaru listings starting at $199.
Search Subaru Questions