FYI,
Swapping engines in a Subaru can be done but it is a labor intensive process. The ecu wiring is integrated into the wiring throughout the dash. You have to pull the wiring from your car and pull the wiring from the donor. Then pin out and tag each wire to match them up. It can be done. Most speed shops charge up to 2 days labor just to pin out and tag the wiring.
See example.
https://images.app.goo.gl/Rk1m62CHp5QDtcQy8. I would be more inclined to build the 2.5 with upgraded internals. I’ve seen turbo Subaru rally cars and built na Subaru rally cars. The difference is that the boosted cars need rebuilds every couple of events. The na cars last for years. There was a late 90’s Impreza that had a swapped built h6 engine in it that had been through 3 or 4 owners. Because it was the 2 door model and was lighter, it would hold its own even against the newer subarus.