A very interesting thread, gentlemen! I am new to the forum, and with your permission, would like to add a couple of facts: B-29s, indeed, would be a disaster to operate from Attu with its mountains and short runways. This is why an airfield at flat neighboring island of Shemya was built...
I've spoken with people from the Kurils about these photos. They said that vegetation and landscape on the pictures is very different from the Kurils, and it looks more like Mariana islands.