I had also spotted the Hofbräuhaus, having been there a few years ago, but had come round to thinking that the initials HB were relevant, rather than Munich. Hofbräuhaus has become an international franchise, and its logo consists of the conjoined letters H and B (as below).
I have spent a lot of time looking at Car X, which looks like a mid-1930s Morris, but with a different radiator, which also looks to have been moved forwards by about 20 to 30 cm. I eventually found some other photos of it, showing that it had been converted to steam power (hence the radiator is actually a condenser). These showed a UK registration number FBP 698, and on checking the DVLA website (UK Driver and Vehicle Licensing Authority), it is registered as "HB Steamer".
So I think Car X and Architecture 8 are linked by the initials "HB", but I am currently unable to link an "Extra" to them.