If it's a braze on we're talking about a steel frame. It's likely to be strong enough, I'd be surprised if it isn't.
As has been mentioned numerous times now it's the heat I'd be worried about, but thinking about it you're not likely to be able to apply a great deal of force with a friction shifter so you could be ok. I think you're going to have to experiment and let us know how you get on
As has been mentioned numerous times now it's the heat I'd be worried about, but thinking about it you're not likely to be able to apply a great deal of force with a friction shifter so you could be ok. I think you're going to have to experiment and let us know how you get on