So I've already got the EJ25, from my legacy, sourcing a 22 block won't be hard. Head gasket is tricky to me, where to modify it for oil lines ect. Also engine management, should I get a megasquirt? 
  
http://www.ultimatesubaru.org/forum/topic/149590-anyone-built-a-reverse-frankenmotor/ I read through this thread which is quite good except there's some things I diassagree with 
  
ej22t crank & rods -- same as the non turbo ej25 (NA) block halves. The whole point of this is to use the ej22 short block ej25 DOHC heads ('96 with hydro adjusters) -- should be able to just use my heads newer EJ25 flat top pistons -- Aren't my current pistons/ the 22's pistons sufficient? ej20g intake manifold with 440cc injectors  -- One of the 2 manifold I have will be good, no? 
vf8 turbo (ej20g) ej22t exhaust (until I put the downpipe in) ej22t fuel pump 2002 WRX top mount IC ej22t bypass valve (I replaced with the TurboXS one) ej22t ECU & wiring harness. original ej25 harness/ECU is gone, and the ej22t ECU sits in it's place, and is all wired in, and I can check code like normal (ej22t way)  -- I shouldn't have to use a 22 turbo block, can just use a normal block, almost the exact same. So the wiring harness mesh is moot then, right? 
  
Would absolutely love to do this build, but need to have all the parts before I do the biuld, and have as much of it pre assembled as I can as it's my dd.  
  
Thanks - H