Most STI engines are solid lifters, the WRX motors are hydraulic, could be done in the car but to be honest it would be a complete pain in the arse i can drop a Subaru engine out in 1hr then its a doodle to do, be aware if they are solid lifters you adjust them using shims and its critical you don't get the exhaust side mixed with the inlet as i did the first time i done it !