1. I don’t see road wheel spacing that indicates a Chieftain.
2. I don’t see rear Chieftain exhaust ports. In fact I don’t see exhaust anywhere, and the only side we can’t see of the vehicle is the left side where the T-90 exhaust port would be.
3. The road wheels in the Iranian photos look more like T-90M/S roadwheels in this photo than any other example I’ve found today. http://i1085.photobucket.com/albums/j424/dickyf4/2013%20Blogpics/T-90MS-tropic7camo_zpsd65be830.jpg

4. The rear of the vehicle matches T-72 and and T-90 chassis down to tow cable placement and bolts.