Shown firstly in 1924, thus before Gillett's records at Montlhery, the car then was called the 'Sports Model'. Advertised as good for 85mph plus. It was renamed the Montlhery after Gillett's success in 1925.
In 1924 standard AC cars had two-wheel brakes and high-pressure cord tyres (=beaded edge). The Sports Model, even early 1925, had four-wheel brakes. Cecil May's car could well be a 1924 Sports Model (known as the Montlhery the following year) and had four-wheeled brakes fitted yet beaded-edge tyres or its a later car and Mr May specified beaded-edge (e.g. 1926, the photo date....though the superior balloon tyres were then all the rage). A later photo above now shows two spare wheels, and a spare tyre, insurance for a tough event if using beaded edge tyres. All this would answer why the car is labelled Montlhery on the first photo. Note also the side lights - this 'streamlined' design was only on the Sports/Montlhery models. All points to a 'Montlhery' Sports model, body to owners requirements, 1924-6.
The body looks very well made indeed and could have been built by AC to special order, considering the requirement for Brooklands (car shown in that photo) and competition work. It appears of quality and may be by a specialist coachbuilder, chosen by the customer. AC may have supplied a running-chassis and, just as Rolls-Royce (his other car), this would involve all the front up to the firewall.
For the Monte Carlo Rally there is now a hood - if you can call it that, as there's no way to fit it at the front and it clearly looks an afterthought with mountings through the body(maybe that's why the driver looks so pensive in that shot!). Fancy doing 1500-odd miles in winter with that hood, windforce against it, bearing in mind the 1927 rally was December/January and involved mountain passes with snow.
Great line-up of AC's at Brooklands. I wish that photo was better!
Another photo now shows the number plate better. The numbers look like 3856, the last two were obscured in first photos. RO3856?
Jonto, my car going well - thanks for asking - it was at a show last weekend, gaining lots of attention and many questions. Send me privately some photos of your car when you have a chance.