Interesting attempt. Some things seem to be a little off though.
First of all I can't see why a tank should have skills. It's crew has them. For the sake of the rules some do make some sense, like Might to reflect its horse power. Endurance? I don't know. If it's just for the sake of stress then i can see why it might be valid, but some trappings should definitely not apply. Same for Intimidation. Alertness again should be reflected by the tanks crew, same as guns. For simplification it is alright I guess.
The stunts largely seem O.K.
Now Powers are tricky. If you go by the rules you definitely have to add a catch to the toughness, like "anti tank weaponry" or something like that (witch would include all kinds of high powered magic of cause).
An other thing is, that I can't see the main gun, witch is a guns weapon in my opinion, benefiting of the might powers. Surely this is nothing that profits from the horse powers of the tank.
Where does it say that faerie magic is ineffective against irony targets? If there is such a rule i'd be happy if you'd point me to it. The "Made of Iron" power is highly questionable as there are no similar mechanics in the game that I know of at the moment.
The Physical Immunity needs a catch as well. I'm also not sure about the discount you award for it (not that it matters
)
The machine power again only seems valid if you see the tank itself as a being. It highlights the problem that this writeup presents. Ultimately the tank isn't a being of its own. It is an heavily armored vehicle/weapon system that provides it's crew with special and power full benefits. That said, some stunts and powers doesn't seem to make good sense. Sometimes it seems you see the tank as a "being" of some kind, in other places you do not.
If I would use a tank in my game, I'd probably treat it as a peace of equipment, that benefits all of it's operators who'd have to do a lot of teamwork actions. It would have a high weapon and armor rating, would provide most of the benefits by means of narration or by providing aspects to the crew. The crew on the other hand would provide the skills that are necessary to pilot the tank, witch might be modified by the tanks computers and electronics. I'm not even sure if I would give it a normal stress track that benefits from endurance and toughness powers. The rules for barrier ratings seem to make a lot more sense to me when it comes to heavily armored vehicles.
All in all I think it's almost playable but some things need tweaking...