Hi Tim, I’m glad you posted this here, as otherwise it would get lost in the noise ‘elsewhere’. I think the reason why you can’t find many photos of the fully enclosed version was that it only existed in prototype form & never saw operational service. “All” the photos that I’ve seen of the real thing are of the same vehicle, taken in the same session whilst at Bovington for evaluation. I do have a reference somewhere to support that but it’s buried in storage at the moment.
The enclosure was just too small for practical benefit & accordingly production versions largely did away with it. Here is some detail including plans for the turret. http://www.britmodeller.com/forums/index.php?/topic/235001267-crusader-aa-mki-bofors/
From that link, the second vehicle shown was known as the “40mm SP AA Gun (Tracked). It was a completely different design and they were built at Mill Hill in London alongside the very similar triple 20mm (the 20mm SP AA Gun [Tracked])”. If you look closely at the photo you can see that it has a standard Bofors gun shield, with attached side extensions, rather than a bespoke design.