My '68 Mk2 came from Stewart & Ardern in West London
Did it? I don't wish to spoil your day but as a former S&A employee I can advise you that Stewart and Ardern were the main Morris distributor for London. This means that they supplied all of the smaller Morris dealerships throughout the London area and it is therefore more than likely that they didn't actually sell your car to the first owner but would have obtained it for a smaller garage. It may say S&A Acton on your Heritage Certificate but that is only the destination from the factory. If this car is registered WMU 211G that is a London Central registration, cars registered from Acton were London North West registered.
I keep meaning to have a look to see what's there now, probably long gone by now - managed to get some repro S&A stickers recently though and have just won a genuine interior dealer's badge on ebay...
Yes all signs now long gone. S&A became part of the Henlys group.
S&A never had window stickers like that, there were window sticker but of a different design. Had S&A actually sold the car, your dealer badge would have more than likely have been fitted under the bonnet not inside the car. Reproduction badges appear on ebay from time to time. Your 'genuine' badge looks in far too good condition to have been fitted to a car previously.
Your Mk 2 Mini has the lower dash rail padding from a Mk 3 or later Mini.