If you ever make up the covers for the CD engine let me know as I need one. Despite the fact that one cannot use an air filter with it - the reason mine was removed no doubt.
Not sure what Lister was thinking with that design...
No engines had air filters in those days, even the CS engines only had a little bit of gauze to start with.
It was farm work that started them off on filtration, that and dusty industrial applications like rock crushers and the like.
The CD and CE just a had a little snout out of the rocker cover, nothing else.
Peter