can i swap a double overhead cam for a single 1998 2.5

AFAIK you cannot just swap the motor. 98 was DOHC and by itself. Then 99-04 are either entire swap or long block compatible. 05-?? have some differences that are non compatible with earlier models / vice versa. I would get on the forums and do more research. The info is there, for sure! Best regards,

Why would you want to do this? What's wrong with just rebuilding your existing engine? What do you really think you'll gain from a DOHC over the SOHC? The DOHC is more complicated and is the engine that is being scrutinized for burning more oil than normal in the newer line of Subaru engines. Not all new engines are affected, but, unless you are buying a new car with a warranty, I would think that a custom rebuild is your best bet. You never know what you are going to get with an exchange engine.