The car behind looks like a 1.5-liter AFM. We could follow two strings then. I'd make two suggestions coming from that. First is that the event, given the year, was likely to be held in Germany due to the fact that until 1950 German drivers were banned from racing abroad (Hans Stuck drove an AFM abroad under the Austran license, but his car was a single seater AFAIK). Second, the Bugatti was probably of around the same engine displacement to be able to compete with that AFM. My choice woud be T40 probably, but that's a pure guesstimation so far.