Takumar 135mm f3.5 (preset) help with disassembly

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Ring 1 rotates and operates the aperture blades, but there are stops at both ends of the throw. I cannot see at this point what stops it. There was a stop screw that screws into the main body between ring 2 and 3, but I've already removed it. I've also removed the three screws on ring 2 that fix it to ring 1. I can rotate rings 2 and 3 all the way around. I tried to see if the two ends of the body screw apart, but they don't seem to. How the hell does this thing come apart? I can't see anything I can manipulate at this point. It has to have been put together somehow. Please help.