[Marshall V. Daut]

By the way and not to drift off-topic, but during this same May-June, 1931, transition period, documented A-400"s (traditionally considered a late 1931 model, i.e., with indented firewalls) were produced with flat firewalls! I recall seeing at least one such A-400 survivor in a back issue of the A-400 club's newsletter. Maybe more have been discovered since then? I would guess that over 95+% of the A-400's had the indented firewall, though. Once again, without seeing company production records, we can rely only on inspecting surviving A-400's to make this assumption - and there are VERY few such flat firewall A-400's around to inspect! That alone speaks volumes.
Marshall