Reassembling an NA Suby motor isn't really that challenging.
OP, as far as OE mixing and matching goes, you can use stock cams and the stock shortblock from a SOHC 2.5 engine, both of which will help make more power. I don't know of any aftermarket pistons for the 2.2 NA however. There's no simple EM solution either- piggybacks like a PP6 or a complete standalone are all you can do. On the plus side, using an EJ25 block and cams plus a header won't actually require any ECU changes- it'll run fine and safe and still make extra torque.