Thanks for the replies.
I have (only) just realised that the bonnet is sitting on the air filetr!
The current filter assembly is 150mm and I need to loose about 10mm to clear the bonnet.
I have seen on another thread how somebody 'modified' the edge of the filter housing with a hammer. But wondering whether I can go for another filter shape (eg tapered) but dont know how to get it to fit snuggly to the face on my Stromberg. Maybe I will have to make something - could be fibreglass?
Anyone got any other ideas? I have spent many hours of google (stromberg remote air filter) but can's see that there is anything out there?