1999 IMPREZA OUTBACK ENGINE VS. 2000 IMPREZA RS ENGINE
The 99 Outback Sport uses the 2.2L engine while the 00 RS has the 2.5L. That said, it "should" physically fit in the engine bay though you will lose some performance by downgrading to the 2.2. I suspect that some of the plumbing would be different as well. I would suggest checking with a qualified mechanic before attempting an engine swap.
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