i have put headers on a vr6 before, and did not have to even come close to removing the engine, and i don't even own one of those cars. i have also put a turbo on one of them.
for kkambbak9399, it isn't that hard to get to the exhaust system and headers for the IS, the only thing you might have a problem with, is rusted bolts, which i doubt, but it also all depends on how mechanically inclined you are.
Originally posted by QuikVR6:
I'm not sure about IS300 headers, but from experience with VW VR6's most times the entire engine needs to be removed due to the placement of the headers.