The manifold will come off by removing six nuts from the downpipe/manifold join and then removing 8 (? I think) bolts from the manifold/head join. Might be just gasket replacement at these points which is straight forward enough, however if the down pipe has a hole and needs to be removed then I think the steering rack is indeed in the way.ÂÂÂ
Oh if only it was that easy
You'll find that 7 manifold bolts will come out with a struggle, and the hardest one to reach will round off hopelessly.  4 of the downpipe bolts will shear off after some serious effort, one will come off with a struggle and again the hardest one to reach will round off hopelessly!
Anyway: To replace the downpipe you either have to lower the subframe a bit, remove the head from the engine, or pull the engine out.  You might get away with it if you remove the front engine mount and drop it forward a little, then try to squeeze it down the back.
Given the choices I'd go with removing the engine if you have access to a crane, it actually isn't that difficult to do!  The choice as they say, is yours