You will have two size thickness generally a 63mm and 70mm (id go 70mm), if its designed for the s2k then all of them should be the same length and same flange size.
Yes it will fit both ends. HFC's are 80% flow over the stock cat which is 40% flow. Definetly noticable at the top end of the rev range. about $300 from memory.
I had a engine light come because I changed my exhaust and my rev's used to drop constantly, found out the (TPS) trottle position sensor was faulty, once I changed this from another throttle body I...
Think about it from a buyers perspective, would you pay more for a better one? ofcourse you would. This gives the seller more power so I say its to our advantage.
Just make sure when using Driveshaft spacers use 10mm width bolts, not 9mm which comes with the T1R's, they will move around and come loose, speaking from experience.
