I've also been looking at the Caple models. I found the size information confusing; I think the unit itself is 535mm deep, and the install instructions require a cabinet 550mm deep (500mm shelf to sit on followed by 50mm space for ventilation).
The key thing for me will be how the back of...
Have you found an alternative oven yet?
I have exactly the same problem. I have the gas hob pipe running down the back of my cabinet, restricting depth to 535mm.
I too was looking at a Caple oven as the depth is reported at 535mm, but was worried it wouldn't fit without touching the pipe...