Frankly, I don't recommend using 3dANALYZEtoAFNI any more. AFNI can now read ANALYZE datasets directly, so no conversion is needed. If you
do want to convert to an AFNI dataset, then (using the fact that AFNI programs can read ANALYZE datasets), something like
3dcalc -a zork.hdr -expr 'a' -prefix zork
would work to write out files zork+orig.HEAD and zork+orig.BRIK. Note that 3dANALYZEtoAFNI
won't do this -- it does something uglier (i.e., creates a .HEAD file that points to the zork.img file, with not .BRIK file).
bob cox