I responded to your other post, but I figured this would help stimulate more content too...
Personally, I wouldn't put that block and those heads together. I WOULD use that 2.5L SOHC block to mate with 25D heads though. I think a lot of folks do the EJ22 heads/intake on 2.5D block. I've done that, and I wasn't very impressed. The heads do not flow very well, and power was lost above 3500 rpm for me. Lots of Low-end torque, almost like a truck though. I am now running a 2.5L block from a 2001 Impreza (SOHC) with heads from a '97 Outback (2.5L DOHC; Found the heads for $600 reconditioned from SuperRupair in Boulder, CO. I'd call and talk to Doug. See if he has anything on hand. Their used warehouse is worth a visit. They have shelves, 10-foot tall full of 2.5L heads, and anything else you can dream of. I'm not sure if they'll ship, but it's worth a shot).
+ STI MLS headgaskets. The power is above and beyond what the other motor had. It has consistent power/gain/pull all the way to 6000 rpm. If it wasn't in a legacy wagon, I think it would give some stock wrx's a fun run. Whatever you do though, the intake/heads have to match the wiring/ECU. So for anything pre-SOHC you need that spec intake/heads...My legacy is also a big pile of rust now, and I'm looking to move the motor to a donor. I'm constrained to pre-1999 though with this intake/heads choice. Once you go to SOHC-land (post-1999), I'm unfamiliar with what can be used for high-compression builds.
Greg