Here is a collection of info I gathered whist looking at my options. (Cut and pasted from various sites.)
In the end I ended up with a standard length inert as I was going to get into clearance issues with the coilovers and my 17x8.5 fronts.
Links -
http://www.turbosport.co.uk/showthread.php?90796-Strut-inserts Here are the rx7 bilstein inserts -
http://eshocks.com/bil_Ind.asp?VC=3Q46&SubChar=Q Mazda RX 7 1986 ?92 = # 8641-1200 ? 50mm shorter
It is mounted through the bottom of the strut via a 12mm bolt, that threads into the bottom of the insert. This means the top nut is dispensed with. A sleeve will have to be made to centralize insert at top and some way of keeping the road grime out is also needed. It is approximately 50 mm shorter than Capri unit. The strut could be cut in half, sectioned then re-welded back together to use top nut if desired or a spacer could be made to move insert up strut tube to adjust droop and compression settings.
They are externally top adjustable rebound only.
Toyota Camry -
Celica 09-93
8641-1211sport 30mm shorter http://classic-ford.org/forum/topic.asp?TOPIC_ID=10915&whichpage=3 Porsche 924-993-968 = # 8641-1038 These are also bottom mounted. The insert body is 355mm long, 42mm in diameter. 20mm shorter than STD. The damping rates are approximately 15% stiffer due to the extra weight placed on them via the car. This would be better for a stiffer spring. The body is not short enough to facilitate substantial car lowering. Externally top adjustable rebound only. Koni Motorsport [Road course] = # 8611-1256 [307mm long insert 45.5 mm diameter. This is a special. Used mainly in European Touring cars. Double adjustable. Comes in various lengths and valving.Double adjustable.Requires top nut for fitment. Various valving optionsKoni Motorsport [Road course] = # 8610-1149 [330mm long insert, 43.5 mm diameter] Externally adjustable. Rebound only. Various valving options. There are plenty of others out there that will do similar, depends on your budget or what you can find.
Rav4 and volvo inserts are also common.
Shaun