With Conkeldurr, I wouldn't worry much about Gliscor as I would Reuniclus. You can actually beat some Gliscors, depending on the set and team. Of course those Substitute/Protect Gliscor wins out if they have TSpikes support, but if it's just run of the mill Taunt/SD, then Conkeldurr definitely has a chance.
It's obvious Conkeldurr will Bulk Up on the switch. This next move determines everything. If Gliscor Taunts while Conkeldurr spams Payback, than Gliscor can loss, seeing as how it's still taking a healthy what, 39%? The next turn it has to SD and takes another 39%. Now it finally gets to attack but by then Conkeldurr can 2HKO with Payback while Earthquake takes 3HKO to kill the Conkeldurr at that point.
If Gliscor uses SD while Conkeldurr Paybacks, then it wins cause it can 3HKO the Conkeldurr before it can 3HKO Gliscor. Of course if you SD and it Bulk Ups again, then you definitely lose. So it really comes down to the situation you're in within the battle that determines which route you take, but Gliscor is hardly a complete hard counter to Conkeldurr. The slow ass Psychics are a way bigger issue.