I have a few quick questions on the use of clustsim from 3dttest++ to do nonparametric permutation testing to correct for multiple comparisons.

First: not all slices within my mask have data from all participants due to slight shifts in slicebox/brain sizes, etc., and I'm wondering how 3dttest++ and clustsim account for that. I like the idea of using 3dttest++ with the -clustsim option because it's agnostic to the fact that there are different degrees of freedom when doing permutations (the helpfile for 3dttest++ says that -toz is automatically turned on when I give 3dttest++ the -clustsim flag, so the cluster defining threshold is based off of the z-stat (rather than the t-stat, which is dependent on df)). Can the cluster size threshold output of clustsim then apply throughout the entire brain (e.g., even in those slices that don't have data for all subjects)? That is, if I want to visualize in a different program (I know, GASP!), would I need to threshold on z-stats (selecting as my threshold the z-stat that corresponds to the p-value that I want to use as my cluster defining threshold, e.g., p<.001) in order for me to use the cluster size threshold output from 3dclustsim to validly control for multiple comparisons? Or would it be sufficient to threshold on t-stats?

Second: Is this approach different from randomise in FSL? Or is the main difference that the underlying stat is a z-stat instead of a t?