The stock ECU works just fine in early-mid 90s subarus whether bone stock, cammed or embiggened Frankenmotor style. Run all the sensors, and an intake and/or header give no trouble, as the stock map will adjust air/fuel ratios as needed. The stock unit also gives good idle (so long as the idle-air control valve and the vehicle speed sensor are good). If you get all the wiring and fiddly sensors andplugs and whatnot out of the donor car it’s the efficient way to get a reliable 140 (stock 2.2)—185 (cammed Franken 2.5) hp at 5500 rpm, with easy revs to the limiter. Downside: the 1995 ecu limits you to 6000. All other years are higher.