Hey Stan, try to find something that will penetrate rust. Mine weren't that bad. I sprayed them down every evening when I got home for about a week. They were very tight be came off without a problem. I think the stuff I bought I found at a tractor repair place called "Rust Away".
On another note, when you start to remove it (the old housing) you will notice that two of the four bolts will contact the turbo body as they are being removed. Use these two to "push" the old housing away from the body of the old housing. I didn't do this with mine but right after I spent the better part of a day figuring out how to get it off someone else posted this method. I removed the entire turbo to get it out on the ground to wrestle with. I started out slightly tapping on mine with a rubber mallet. To finally get it off I had to use a wooden block with a fairly large hammer to get it loose. Just make sure you don't bind the shaft as you are getting the old housing off. You will better understand the part about the binding, if you don't already, when you see the new housing. Good luck and you will love the new spool up.
What size housing are you going to?? Yours is a 93 so it should have an 18 cm. If you are dropping to a 16 you may not notice much difference. I have a 92 that had a 21cm, and noticed a big difference with mine.