This is my first post so please, be nice / bear with me...

We became the proud owners of a 1981 1.6 T25 with a CT engine about six months ago. I am not very mechanically minded but thanks to the info / posts on this site and an aversion to spending more big money with a mechanic, I am slowly picking bits up.
Anyway, while in the engine bay the other day I noticed the air filter box has an oval opening facing the rear of the van on the right (photo attached, circled). I guess this is where air goes in(?). My question is, should something be connected there? If so what and does anyone have a part number / link? This photo from Google seems to show something there https://i.ytimg.com/vi/I-wyU58BEJE/maxresdefault.jpg
I ask because I discovered the pipes that run from each heat exchanger to the air distributor pipework aren't really held on by anything substantial (need new jubilee clips) and the air distributor part is cracked / melted (new one sourced) where it joins the alternator fan(?) and goes through the tin on the right. The heating pipework and other work on the van has uncovered previous owner(s) neglect so I wouldn't be surprised if a bit is simply missing.
Cheers!