This was going to be my point. Growing up in Chicago it was fairly flat, but many French plain steel bikes like the UO-8s came with cottered steel 52/36, with 14/28 5sp freewheels. Perhaps some smart product manager in France decided "there's wind in the Midwest, all those normal people riding our bikes will need lower gearing than 45/28." I think the design of those bikes was pretty smart!

I don't remember the chainring bolt layouts, however, for the French cranks or the British ones. Brits like Raleigh and Dawes were more commonly 52/45 and such, but with a lot of variation among models, years, and ... the phases of the moon?

As long as you get a replacement chainring with plain teeth and the screw holes in the correct place, the choice of steel or aluminum should not matter very much, so if perhaps Peter White or another shop has the correct ring you have some flexibility.

Caveats: 1. With a smaller small ring and no other changes, you might need a few more links in the chain. 2. With a smaller small ring and no changes, you might need a front derailleur with a deeper cage, in case the chain drags on the tail. 3. If your rear derailleur is near it's wrap-up limits, you might need one with a longer cage.

Something, maybe the craze for valid Eroica bikes, is driving up the market for vintage derailleurs which can handle wide gearing. I'm amazed at the prices for formerly disrespected items such as Huret Allvits, Simplex dual-pivot rear derailleurs, and Campagnolo Valentino and Tourismo, especially the longer-cage versions (the Valentinos do not have the range to be valid replacements for your original). If your original derailleurs are not at their limits, it's probably smart to limit your gearing upgrade to what the existing derailleur can handle without being stressed. The issue with stress is that these are nearly 50 year old parts and they were not the highest-end availalble in the day. If one breaks it can be hard to replace for less than the value of the bike.