Roger, I have 1/8" stamped sheet metal brake drums on my 1933 Continental. The Ruxton had the same drum, only much larger. I think they were both Budd chassis. When I had new brake drums turned on a large lathe I had the braking surface made 1/4" thick and the rest 1/8" to match the original. I, too, had heat dissipation in mind. Being a highly skilled machinist you'll appreciate that the 18" x 3" steel slugs weighed about 300 pounds. The finished drums weighed 19 pounds. I was there on day while he was turning them on a 12" swing lathe. It was ringing like a bell while he was cutting. The noise was thunderous. He hauled away barrels and barrels of scrap.
Roger, being in the position you were in at GM did Europe slide into safety standards easier than we did? Technically, no one here that's licensed would risk using oversized drums, under penalty of law and extreme exposure, but I suppose we're allowed to do that to our own car. I'm no mathematician, but wouldn't thicker linings have to be trimmed away more to fit a worn drum. At what point is the shortened shoe life for the thicker lining no longer an advantage? Have I made my question clear?