By this point, I had purchased from Watford Electronics an Acorn 1770 disc upgrade kit and ADFS ROM. But, on opening my BBC Model B, possibly for the first time, I found it was completely different in layout from the description given in the fitting instructions. I wrote back to Watford with a full description of the differences between my Beeb and what ought to have been and asked if they could help.

Here was confirmation that I had been living with an American Model B all the time. I wish I still had this somewhat rare machine today.

I would suggest that with a bit of electronics know-how, the 1770 board could probably be fitted to an American Model B. From what I remember, I think the main problem was the 8271 was not socketed so it could not be extracted and replaced with 1770 daughter board. Maybe de-soldering the 8271 and fitting a socket would have solved this problem. I don't know if this has ever been tried. It could be that the disc interface circuitry is itself different so this would not work.