Hi Lisa,
Where would those spheres be centered, around
the peaks? If so, maybe you just want to get the
cluster peaks (via 3dclust) and then use 3dmaskave
with -dball or something.
If you require the spheres to intersect the original
clusters, then use 3dcalc to intersect the cluster
mask with a 3dUndump mask (from the coordinates).
- rick