After aligning prims, linking prims into objects in SL often proves to be both frustrating and befuddling for new builders. In my book I noted the great forum post from Ceera Murakami where Ceera says "It's difficult to predict exactly how far apart the farthest pieces will be, except by trying in-world".
Recently, I ran across this link http://wiki.secondlife.com/wiki/Linkability_Rules on the SL wiki while reading about the new Havoc4 beta. The beta states changes on link ability as:
Linkability Rules [changes with Havok4]
o More robust: depend only on primitive position and scale (NOT rotation, cut, shear, twist, taper, or hollow)
o Larger linkability distances (proportional to sum of scales, rather than the root mean square of the sum)
When these changes do eventually make it into the main branch it should be very helpful for builders who are trying to link large objects.