Another thing you could try is a spline/12 point key tapped or pressed in with g-clamp - obviously this is a medium drastic option but might be worth considering if less damaging things don't work. Suspect someone's already taken the nice options away from you.
A couple of William Lawrence cabinets (only naming as there were made in my home town) and the classic, can't believe I'm the first to post a pic of one, G-Plan 'Astro' (can't remember what it's real name is).
I have some Manitou's similar to these on a bike and like you I initially thought they might not be up to the job - I'm glad to be wrong once again as they ride really well with minimum faff.
Sounds a great bike, looking forward to some pics!
Not familiar with strip down of those pedals - could you disassemble in situ and then get the pedal flats into a vice? Go on, you know you don't really want to give up! 💪