Do the cat first, keep the resonator.
Then get a used 92/93 2.55" pulley from a member here and scan on a HOT day. You MUST scan in the worst conditions (or close to it) that you plan to drive daily with the setup. You will want an oversized idler on your SC/WP belt tensioner. (3.5")
I assume you've already had the exhaust manifolds off the car to inspect for cracks with a magniying glass, and have checked your fuel pressure with key on, ignition off, at idle, and at idle with the vac line pulled from the FPR?
And that you've read the article in Techinfo for BEFORE upgrading pulleys on a S1?