Yes, the later LTS' and the STS used the same rear end and shock arrangement. I saw that shock on eBay too - I'm very tempted to buy it for my STS but my credit card won't let me
I have a load of shock spares too, as well as a Super Deluxe shock (I can't confirm whether it's in working condition though as I've never used it).
I've got springs, adjusters (rebound and compression), spring retainers (top and bottom), travel chips, mounting bolts and trunnions, as well as spare suspension bushes.
Thanks ba57ards - I'm not sure what I need yet, as I don't know if the shock which is fitted to my STS at the moment actually works!!
I could potentially do with a complete working Super Deluxe though