Lettering, the Marcinelle School Way
This is from an interview with Andre Franquin in the book “Franquin/Jijé: Interviews with Philippe Vandooren”, where he talks about how Morris drew the guidelines on his Lucky Luke art boards for lettering:

Loosely translated: Morris took a comb, removed the teeth where the letters went, and then scraped the comb over carbon copy paper to draw the lettering guidelines over his art.
Franquin made his own contraption:

According to the caption on this photo, “the height of the spans is 3 millimeters and the interval between each span is 1 millimeter.” That seems very small to me, and the lines look very tight in the picture. Did he use two “spans” per row of lettering, maybe?
And, what, did nobody in Belgian own an Ames Guide?!?
I did a little research and found this article about the Ames Lettering Guide and its creator, Oscar Anton Olson. He made the original Ames guides in his basement and did, indeed, sell them worldwide:
Professor Olson founded the O. A. Olson Manufacturing Company in 1919 to produce the Ames lettering guide which sold all over the world.
The name came from the town where Olson lived at the time: Ames, Iowa.
I wonder how many comic creators in France and Belgium used Ames Lettering Guides by the 1950s…
Probably no one.
Until you mentioned it, I had no idea what an Ames guide was.
I can only surmise, that in Franco-Belgian BD, until recent years, the lettering was part of the craft, simple as that, and as such, fell into the lap of the artist. As suck, was unique to a creator.
In the 60s and 70s, most of us avid readers used to be able to recognise the series from the lettering alone, that’s how personal it was.
I can remember in the 80s how shocked I was when it was reported in US specialised publications that John Byrne had crafted a font based on his own handwriting. Mind blown.
And as far as translations of US/UK comics went back then, higher quality french publishers like LUG or SAGEDITION had their own in-house letterer that we could also recognise in an instant. Others, like the digest-sized B&W ones (AREDIT-ARTIMA, MON JOURNAL, …) used mechanical lettering processes, sign of perceived cheapness, in our own eyes.
Now of course, sometimes, personal lettering would enhance the series. Uderzo’s lettering for ASTERIX is still the benchmark. The Marcinelle school had that down to an artform as well, and that one was very consistent all over Spirou house characters, probably inspired by the Franquin method you described.
Other times, it would make the reading more of a chore. As a youngster, I really disliked Morris’ lettering on LUCKY LUKE, I found it difficult to decipher, with its particular curvature of certain letters. Pet peeve of mine, I hate lettering when certain letters touch (remember the FLICK argument in US comics ?), making me pause in my reading, a puzzled look on my face. And a few years later, when the INCAL came out, I really wished that Jean Giraud / Moebius had given it to someone else, cause I found it really repulsive and my first reading of that book was from a US translation when it was lettered by someone else way later.
Hope that won’t get me excommunicated 😉