[39s used round guages same as 37 and 38. 40s used a rectangular guage cluster same as 41-46.]
This is true, however my 1940 School bus had the round dash gauges. I figure since it would have been a chassis/cowl combination, no cab, that Chevy was just using up their 1939 inventory.
Due to modifications I made to the steering and dassh, I ended up smoothing it and relocating aftermarket gauges. (long story)
