It looks to me that the filter is doing its job, and only a K & N could
handle this much load, but some dirt is getting around it between the
filter and the cover plates.  I have this same set up on one of the MGs,
and I notice you don't have the spring clips that normally hold the
assembly together.  The wire ties you are using could soften and
stretch, and even  fall off, so you might see if you can replace these
clips or rig up some type of clamping system with spring tension (Bungee
cords?).

Be sure you wipe off the loose grit from the whole assembly before you
remove the filter so you don't drop some stones down the carburetor!

K & N sells a special grease for better sealing on this type of
assembly, but any multi purpose grease will work.  Just rub a good layer
on the filter's sealing surfaces before you reassemble it.

You have more blow by than I'd like to see, which is indicative of worn
piston rings.

Keep on going, and rebuild the engine when you get back!

Stuart