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If it helps, I just bought a drive side 49d crank that was sold as french threaded and marked as such on the rear of the crank, but when I got it my British threaded pedal screwed right in no problem, didn't even need any convincing to go in. So I think you may be able to do this the other way around, brit thread to french pedal. Seems solidwhen ridden. My guess is the threads are similar enough and the alloy is soft enough/pedal steel hard enough that it just cuts a thread. +Having said that, when I check it it doesn't look like a new thread has been cut so maybe my crank had been rethreaded in then past?)
I have a Stronglight crank puller which you could use.
I also have a 170 left hand 49D , but it's on a bike - I would happily swap for TA.
I also have a LH 49D which needs a helicoil - I can't find it this moment and it's too cold to spend long looking.
Let me know if any of this is helpful.