My advice? 3 words:
DON'T BUY IT.
1. I would never buy a SC without being able to personally inspect it, especially if I knew it already had problems.
2. The upgrade to a 94/95 SC and TB on a 92/93 is NOT a piece of cake, and probably only worth it if you're planning on spending alot of time at the track. Plan on spending at least an extra 200 on a ZZP Mini-AFC controller to get a working MAF.
3. You can probably get the same level of performance by simply changing your SC pulley to a 2.2", and working over your intake and exhaust, which you should do anyway.
Was I convincing? Making noise at shutdown is a new one on me, and it sounds scary. I'm thinking rotor clash. A bad coupler will make noise at idle, but I doubt you'd hear it at shutdown.