I have seen this style before - but only from the front. I did not realize until I saw this particular steel that the entire body construction is different. Unlike any other National-Dobro aluminum steel (including my National prototype), the body is mostly open to the back. There is a cover over the pickup but not the rest of the body. I do not believe these visible chambers were ever covered by felt based on the decorations scattered around the back.
But perhaps the coolest aspect of this particular steel is that it was modified at the factory. The top of the body was cut away, hence the nickel-silver cover now screwed in place over the pickup. This allowed the coils to get closer to the strings, thus increasing the output. For various tedious, nerdy reasons, I am sure that this modification was done at the factory and is not some later change. This experiment is probably what lead to the revised casting with the hump over the pickup.
But note my use of the plural earlier: pickup coils. This steel does not have the single-coil pickup normally found in this model, but rather the hum-cancelling version found in the Dobro All-Electric and a number of prototypes from 1934-5. The output is similar to the single-coil units, though the sound is brighter and clearer.
The jack, pot and tuners were replaced by previous owners; this was known to me and did not come as a surprise. The serial is slightly unusual in not starting with an "A", though it is still a pretty low number. I suspect this served as an experimental unit for a while until the factory decided they were done with it and gave it a number before shipping it out. The case has a false bottom that serves as an accessory compartment, something I have not seen in one of these cases before.
The requisite picture of the old folks' reunion:
