I have no idea on that one. BTW, the rears aren't struts, they are dampers (Dampners?[shocks]), don't know if that makes a difference in your search, or if I am just being anal retentive.
Whats the difference on the lower mount from an s13, to a z32?I would be cvarefull about running z32 shocks on an s13, I would guess that they are valved diffrent. Not sure if that would hurt the performance or not.
I couldn't find anything from bilstein for the 240sx.
Have you checked to see if the Koni OTS rears can be modified for external adjustable? Probably wouldn't be worth the price/hassle, if it can even be done. Here is a list of Koni rebuilders that I know of. And I am not recommending any of them, other than Koni due to "stories" I have heard about a couple of these companies. I am just posting the company's that rebuild Koni's, use at your own risk.
http://www.propartsusa.net/http://www.t ... vices.html
The KYB's are externally adjustable.
You might try contacting Koni, or Bilstein to see if they know of a another shock they offer for a different car that uses the same mount and has the same or similar valving, and are the same length. Because that is basically all you need, if I'm not mistaken, is a shock that is the same dimensions, that mounts the same way, that has the same valving, but is externally adjustable. But I would guess if Koni or Bilstein made such a shock they would sell it for the 240 as well as what ever make/model it fits. Again, none of these custom application would probably be worth the time/money/hassle. But due to the generic style mount the rear uses, there might be another shock made for a different car that *could* work. I am not advocating nor suggesting you do this, I am merely throwing out some ideas. Do this at your own risk. I race with a guy who looked into this that ran a Chevy Colorado, and he couldn't find any sport shocks that where made for his truck, I don't remember if he actually would up running shocks off of another vehicle or not. Or you could *GASP* buy some Tiens/megan/ksports/insert JDM coil-over here.