Rancho/ Caltrac question

[rmk57]

Just wondering what shock to use when using Caltracs. The distance between the shock mounts is 18.25".  The Caltrac people say you need minumum of 4" of extension for them to work properly and compression is what your willing to put up with before the shock bottoms out, which looks to be about 3" based on 7" of overall travel.
Anybody have Rancho part # they've used for this application?

Randy