The cranks are one-piece and the BB shell measures 50 mm. It's huge.
After a closer inspection the derailleur is not in as good condition as I initially thought. The lower of the small cogs on it is worn through and does not hold the chain at correct place. This makes it nearly unrideable in current condition. The springs are also quite soft. I know that there's one period-correct NOS Huret derailleur in a LBS. Buying that might be the easiest way forward with the gears.
I took a look underneath the silver paint, and there is chrome on the rear stays and fork.
Here's a picture of the headbabadge.
