Hello,
I have recently seen a friend's 850 Commando, and the bike has in original equipment a cartridge filter, like the one you speek. The interesting detail is that it is fitted BEHIND the gearbox, under the bottom oil tank level, and not in an upper position, althought there would be a lot of place... (not speaking about the mud there and the difficulty to change it)
The idea is that Norton's people had the same troubles as your's, and even with upgraded, and simpler (in comparison with the A10) oiling system, there was no other solution to locate the filter, and make it work properly...
I intend to fit a filter, the cartridge type (I'm french, and the cartridge is the same as 2CV Citroën), but will try to locate it as it is allways "submerged" by oil.
Cheers, Claude