Yes you can keep your powersteering. Just swap your existing pump over, or use the pump that comes on the 20v. I'm sure its not too hard to swap the stuff over.
You can use your existing exhaust manifold, but you need to slot out the 2 outer holes. But it would be nicer to use the 20valve exhaust manifold, and if it does not fit the rest of your exhaust just take it to the exhaust shop, not a big job.