Tanking heroics is pretty much the same as tanking in raids, except it's downgraded. So all the usual tanking stats apply, but you don't need as much of 'em. Def cap is 535 for hc bosses but other than that, don't need much else. You can maybe gear more for trash, since the usual time when things go wrong for tanks is during AoE. So get tier sets that focus on those abilities. For old wrath instances, you don't really need that much health. Originally I would tank them all with no more than 25K and hitting 30K HP was a lot on those days, and many of those instances have actually been nerfed since. Plus that assumed that DPS and healers were in similar level gear. The Icecrown HCs need a bit more but HC farming will yield you with ToC level gear so that's not an issue either.
So all you really need to do is continue doing HCs and you will outgear them all in no time.