Far be it from me to tell people how to compile their kernels - especially with Crux-ppc!
However, I found the following site useful, which also provides de-blobbling scripts to clean out your kernel should you feel the desire to do so:
http://fsfla.org/svnwiki/selibre/linux-libre/
I have also transplanted both Ali Gunduz' kernels and Robert Millan's kernels for Debian listed on that page into both gNewSense and Ubuntu without too many issues. What is exciting about Robert Millan's offerring, is that he provides PPC libre kernels, although currently only up to 2.6.26. The repos are listed on the site above, and the exciting notice about it:
http://lists.debian.org/debian-devel-an ... 00010.html
Obviously the de-blobbing scripts will likely be more useful to a Crux-PPC user.
Full-disclosure requires me to state that I have not personally de-blobbed a ppc kernel with those scripts. AND, I'm not trying to start a political issue - just a notice of availability that might be of interest....