Considering that Gliscor has no chance against a non-STAB Ice Beam and has trouble dealing with even a special grass move, I'd say that there's no point in giving it any investment in sp. def. Of course, 31 IV in any stat is nice, even if it goes unused most of the time, but all things considered Gliscor has much more chance of surviving Ice Fang than it does Ice Beam. Go for the one with perfect defence IVs.
If you give it some speed investment, it should be able to set up Substitute before a lot of threats, so it PP stall & wait for an opportunity to use Toxic.
Another option: don't evolve Gligar (if you haven't already) into Gliscor. Give it an Eviolite an let it be a Toxic/ Roost stall.