Hi-
I stole the recipe for doing this, below, from what afni_proc.py would do if you included the option "-regress_run_clustsim yes" there (and why not have this done in your processing that way?). In the output of afni_proc.py processing, the generated script would essentially use the following to store the 3dClustSim results in your output stats* header for you.
Add the following option to your 3dClustSim command:
-cmd o.clustsim.acf.cmd
... so that a 3drefit command is generated+stored in that output text, to be applied soon after.
Then, add the following commands to your tcsh script file, after your 3dClustSim command:
set cmd = ( `cat o.clustsim.acf.cmd` )
$cmd DSET
... where DSET is your dset of interest (such as "stats.$subj+tlrc"). This essentially runs the script from o.clustim*cmd to dump information into your DSET of interest.
--pt