We have a 1929 (I think) yellow rumble-seat convertable at the museum.
The V12 is OHV whereas the later V12 from 1942 was flathead.

Do you remembers why?

Answer:

The hood of the older one was narrow,so a flathead, even with the 60
degree, angle would not fit., so the valves were made to be overhead.
On the later ones, the hood was lower with wide fenders and the 120
degrees engine was wide so flathead design, even though more primitive,
was use. It was also chaeper amd quieter.

Karl (Via mail2web as my computer is down and I am guesting on the one
on the other side of the room) Haas