@juggle, I’m interested in having constraints for the FABRIK node as well - add me (same name as on here) on the UE4 launcher or Steam and I’ll try to help if you’re stuck.
It looks like page 250 of the FABRIK paper describes how to do the constraints properly for this particular IK scheme - pretty interesting actually, moving the target within the constrained area rather than limiting the joints themselves. I like that more anyway, it should be far more stable 