Hey, I can help you out with some of this,
Mercedes SL60 AMG:- Owned by MK same person with the stingrays and the red firebird trans-AM and green boat-tail buick, driven rarely.
Ferrari lusso:- read about it on pakwheels only can't find the post though, it was owned by the zehri's, still have it, ownership is disputed.
Dunno much about the other two ferrari's except that one was sent back outta the country because the duty was not paid, but this may not be true as I've only heard about it.
Dodge Stealth:- Blue one that was in khi in mid 90's? It was sold to someone in Islamabad back then only. last I heard of it.
Are you talking about the purple SL?- if yes then it's still in khi, I've seenit on the roads quite a few times as of recently.
Viper at park-towers is still there to the best of my knowledge, the other red GTR in now in islamabad. Was owned by a car enthusiast in khi, he's got a couple of more gems but all modern day creations. is the other viper that you have in mind black? I've heard that it is owned by a Doctor but I've never seen that car.
The 90's magnum was as I've been told owned by a fuedal family, have no clue about where it is now, I'm talking about the Black one with red stripes and all, sounded like a plane! Last I saw it was in early 2000-2001.
No clue about the other 2.
If you find out more about the stealth please let me know.