This has been bugging' me for too long, gotta ask

I have two full sets of engine tin.. both 914 type 4. One is 2.0L and the other is 1.7L. I've been wondering about the 1.7 tin - what is the "square hole" in the rear part of the top main piece (it's on the driver's side)? it's a factory made square hole that sits down in the area between the #1 spark plug and the rear vertical firewall section... it look to maybe direct air (my guess) down under the tin via a sheet metal tunnel, to the oil return tube for #1 ? The 2.0L top wing section does not have that hole, and it's vertical piece under the tin is the same BUT does not have the built in tunnel.

Someone ed-u-mi-cate me !

Early 1.7 used a oil bath air cleaner that used engine heat via steel (below) & plastic (above) ducting on the L. side to presumably heat the oil ~? There is a specific rear engine tin piece(s) that mates with the top tin section you have with the cut out.
Nowadays kinda hard to find as 1.7L's weren't the 1st choice to restore.

I have the oil bath air cleaner pieces (uninstalled atm, since I've owned the 1.7) AND the pieces that mates to the square hole is already attached. But is there a connection piece between the square hole and the oil bath air cleaner? square on one side and round on the other maybe?

The plastic piece referenced above

Oh yea, you did mention that - thanks!

I have the large rubber U-shaped plenum hose.. I'll find a diagram and see if there's a piece Im missing. Thanks again.