I have replaced the broken TU lever on a 66 and have the remains of one that came off our FW. Both of them show what looks like crystallized metal at the point of breakage. I would say from that, the take up levers are made from a very hard borderline brittle steel.
They'll bend once, but break when you try to straighten them.
I'd make sure to have a replacement handy just in case, then I'd heat it cherry red at the bend to soften it before I straightened it.
Even then, with my luck it would probably break on me.
Joe