First off, there were three different air cleaners for Mark V.
The 2.5 Litre used C.1808 (AC1579005).
The 3.5 Litre first used C.2594 (AC.3755) and later C.4507 (AC.3873).
Your second filter, the one missing the mesh, appears to be the same as mine for my 3.5 Litre, but I don’t know which mine is. It looks like they took a short one and made it a bit longer by adding a section, so maybe this might be the difference? Is one of yours longer?
Here is mine:
The part you need is called Air Intake Pipe. Some people call it a plenum.
The 2.5 Litre used C.2817 and the 3.5 Litre used C.2818.
I imagine the difference is how they fit with the H3 carbs vs the H4 carbs, and possibly the inlet diameter to fit the different air cleaners.
Here is mine for my 3.5 Litre:
Notice the angle on the bottom rear corner. This is to clear the steering column on LHD Mark V. These things collect oil from the rocker cover breather so there is a tiny drain hole in the bottom.
The Mark IV parts book lists air cleaner pipes C.1789 and C.1790 for both RHD and LHD cars. I wonder is that a mistake, or did they make a further change for Mark V?
Finally, as you are shopping the used parts market, be sure not to buy one for a Mark VII, as they will not fit. The carbs center to center spacing is different.
Here is one for a Mark VII:
Notice the extra breather holes for the H6 carbs.