Great replies! Thanks to all who've replied.

I'll keep the new shoes, likely take straps off my Atoms, leave the toe cages; they're a fairly late addition anyway, the original steel ones got kinda rusty after ~ 30 years so I bought new plastic kind.

JDT thanks for that pic! Seems my arms were made before Stronglight had need of stamping thread specs. There's naught like what's in that pic anywhere on either of 'em.

Simple test'll be try one of my Kona's pedals, or a 9/16x20 threaded bolt from the bin @ work. Easy enough either way.