Many thanks for pointing out this auction item and you are quite right---it should be in the register. The idea of the latter happened after the date of this sale and is the reason for it not being picked up. I appreciate the alert. The sale particulars refer to a goose-neck tonearm but it is a swan-neck seen in the photos. The tonearm rest looks to be wooden which was often a feature of the Xa model.
So, it certainly looks like a Xa to me and I think it is important not to be confused by the motor or turntable etc as customer choice was usually king. Various options were often available from new. Additionally, original motors were often superceded or changed for any number of reasons---particularly with the progressive advent of electricity into private homes throughout the nineteen-thirties.
The telling detail on this particular base unit would appear to be the bronze plaque which perhaps suggests 1932 if I have remembered correctly what Frank James told me. I am in the process of double checking the statement that "bronze plaque means 1932" and will report back as soon as I am able. The only other example I have seen with the bronze plaque is on the deckboard of a Xa owned by Frankia which is #412---I have asked for photos which should arrive soon. It is perhaps interesting to note in passing that the second number issued to the Cobham Hall example is #333 (formerly #199) but both plates are made from ivorine. We may be starting to produce a larger picture but more detail is needed.