I don't believe they are much shorter, if any. They use a different durometer material to work in conjunction with the lowering springs. I specifically asked a Ford Racing engineer about this at the Carlisle Ford nationals and confirmed they are a unique part. Although I've also read it's just the GT500 bumpers.
Some people just cut them down but (unlike the old days) these are actually an active part of the suspension. They are essentially a foam spring designed to help dampen the suspension as it reaches the end of it's travel.
Well I plan on upgrading my struts after the new year, and don't really want to disassemble my front struts again (bad experience last time).
Will aftermarket struts already have something like this on the assembly? Or would I still need them with lowering springs?