heres my suggestion , rb30et bottom end, put your rb25 head on, aftermarket ecu(do some research, i recall someone telling me rb20 ecu's are easy to interchange(well i was told rb20 turbo set up with rb25de engine and rb20 ecu)) add a nice big cooler stock rb25 turbs full zorst upgrade the fuel accesories dr drift tune and youll have a torque monster i think i answered some of your questions in there somewhere too . headgasket change would be advisable though. if you want 140 rwk just slap an rb20det in, youll love it, trust me lol