On the Miller engine, the plate on the side of the crankcase with the oiler attached is also stamped "STUART". It looks like the AE evolved. My copy of the TEE reproduction of Caunter's " Model Petrol Engines" shows a twin AE with top end similar to the single pics that Jason has posted
However, the " On the Wire" website has a picture of an earlier air cooled AE twin which shows an automatic inlet valve and the same cylinder head and cooling fans as the MIller example
The image data suggests this is from 1910. The picture below seems to be an early water cooled AE single with the same cylinder head and auto inlet valve
The next question is: Did Stuart actually make any or were they all supplied as kits? I guess early issues of ME may supply some adverts but my collection only goes back to the mid 30s
Rod