on 2nd gens the SI rack uses a progressive set-up and the rack and pinion from a DX will not fit into the housing of an SI.
or so i was told... when i was putting my quaiffe rack in there, i didnt have much time to check things out as i had to drive to work soon after (i was nearly late because i had trouble getting the assembly back onto the car). i wish i had looked closer at the dimensions of them both, but from the info i gathered, the DX rack is either larger, or smaller than the SI rack and so it wont fit properly into the SI housing, and vice versa.
they both mount up to the cars though, without any problems