Hi Alvin, I had a look through the booklet again and recognise the parts numbers etc, so at least your copy and mine match up.
Naturally, as my units are in place and the under-tabs now hidden, I can't see these fixing locations. It's possible that I looked at the diagram for cannon locations to ensure the barrels protruded through the wing ports correctly and simply made a trimming correction for the underside locating tab if it wasn't correct (by this time I'd seen a few similar issues arise so wasn't too fussed about such a correction.).
Broadly speaking, the port cannon have their feeds (the U-shaped arrangement moulded adjacent to each cannon drum) to the left of the barrels, and the starboard units are fed from the right. The ammo boxes (Steps 117-20) are placed adjacent the U-shaped feed in each case.
On the wing bed itself, the four small rectangular plates (two parallel rows) are the points of contact on which each ammo box is placed. In each case, port or starboard, there is a further part (F04 port, F03 starboard) that fixes behind the inboard of each cannon pair to the nearest structural members (steps 123 and 124, on my plan).
Not sure if this was what your query was about, exactly, but in terms of left/right placement, these are the details as I found them.
