Sorry about the health, hope you're getting better.
I'm feeling a bit sick myself now, but fortunately only mentally!
I assembled the stowage area/upper helm, carefully painting areas which I wouldn't be able to get to later. Looking at the mast support boxes, I thought I could make a better job detailing the port one underneath the air intake, cutting four small slots. When I came to fit the completed stowage area/boxes, I found that the whole assembly was too tight high up and forced the GRP sides of the cockpit slightly out of line. I tweaked as much as I could but there was still a discrepency, but as it was all glued up, I left it...but didn't like it.
This morning, first I read your post and realised that I should have fitted the brass mast support brackets as you explain, then I found the perspex detail sheets for around the air intakes included in the kit and I want to use those, and what with the misalignment......I took the whole lot out! An hour with my Dremel and a sharp chisel....and no harm done except to my pride. I'm going to start again.
There is a smaller air vent supplied for the starboard mast support box (s/a 34), but I can't see one on any of the reference photos in the cockpit. Is this the one that shows on the outside (starboard side) of the cabin moulding?