Now I'm a Pro I have time on my hands - none of the frenetic scramble to answer quickly before anyone else !
I've been thinking about this one. The engine is 2.9 litres, which suggests either an 8CM3000 or an 8CTF. The latter car was very much a monoposto, and went on to success at Indianapolis, but the former was effectively a "production" racer, and was available, more to the point, in two chassis widths, 620mm and 850mm. The latter size was extremely amenable for conversion to two-seater format.
In 1933 the British-domiciled American amateur Whitney Straight ordered 3 Maserati 8CM cars from the works, one of which was to be of the wider size. The interesting thing is that he arranged for Thomson & Taylor at Brooklands to carry out some engineering alterations to the cars, which included fitting pre-selector gearboxes. (Doug Nye states in a brief resume of these cars that they were Armstrong-Siddeley 'boxes, not the Wilson mentioned in the "ad"). In fact only 2 cars were delivered on time, and he was later provided with his third car which turned out to be an ex-Nuvolari works racer which had been refurbished (typical of Maserati shenanigans).
The wider-chassised car was #3012. A similar car #3013 was delivered to Lord Howe. This was crashed by a later owner and the remains were recovered and restored to original in recent times. However, Straight's car #3012 WAS bodied as a two-seater sports car for the road, albeit in typical pre-war cycle-winged form. It no longer exists - all that is known is that it was broken up post-war. I'm working on the premise that this puzzle car was bodied in the UK in typical early-50s style, converting what was an old-fashioned design into something more streamlined and in the modern fashion. It's what happened to a lot of old cars, even what are now considered historically important and valuable racers.
So I can't answer the puzzle, but I'm inclined to think it is Whitney Straight's chassis #3012 which was always a road car, and was modernised after WW2 by a new owner. There were no other Maseratis made with that engine size, and I really can't believe that a second-hand car dealer would go to the bother of importing a car from the Continent just for resale. The car must have already been in the UK, which makes it almost certainly one of Straight's cars.
