That's a very cool bike. If running a TA triple, why not find TA british threaded bottom bracket cups with the right spindle (the spindle will be marked 374 and the length is 123.5)? Those tend to have pretty narrow Q factors though and those stays are bowed out so maybe that will not set the crank arms far enough out to clear the frame.
Also why do you think a TA crank is ISO? Sutherlands has it as JIS; so does this site which has a good discussion,
https://www.renehersecycles.com/bott...s-demystified/
I know you want to go all original but I'd be tempted to run a shimano sealed square taper BB (or something fancier if you like). Just find a shop that is OK on returns because you may have try out different BBs until you find one that works.