OEM air cleaner box or aftermarket?

Hey folks, first and foremost, Im new to this whole “two wheeled vehicle” thing so sorry if i end up providing everything but the useful info so I’ll just give you all I know. 
Kz440a (i think). Chain drive, air cleaner box is either an a or d model according to the manual i found online. Not sure what year exactly but willing to investigate further if you think it will help. 
 The question: i currently only have the main box with the rubber boots that attach to the carbs. There’s two rectangular holes on the other side that i can see straight through into the carbs. After looking around online it turns out there should be another part that bolts onto that which houses the air filter (again, correct me if I'm wrong, I'm going off what i can see in already sold eBay listings, and the black and white manual). Is it worth finding that box and filter on eBay or elsewhere or just getting aftermarket filters? Im in no way worried about keeping this thing original, it’s a bobber (i had to look up what that ment) project that never got finished so it’s already chopped a bit. 
I got it to fire a few days ago and run on starter fluid since im still working on a pinhole in the gas tank, and im absolutely stoked that this thing actually lives. 
Let me know if y’all need more info, or have any tips and tricks for working on bikes in an apartment parking lot drinking Irish coffees just to beat the cold long enough to fiddle around with the points system a little longer. 
Thanks folks!

the stock airbox is the best way to go. but are hard to come by. the 440 cap tends to get tossed. on some models because it gets broken. there are mods you can try to get the individual pod filters to function. instead of just connecting them directly to the carbs as is. someone came up with a 3D printed airbox but the plastic didnt hold up. I think that was the problem.
1980 KZ440-A1 Ltd >> www.partzilla.com/catalog/kawasaki/motor...a1/air-cleaner-80-a1
edit: a number of 400/440 models used the same airbox.

Awesome, thanks. I’ll keep my eyes pealed for one online. Ill still probably keep looking for workarounds in case I can’t find one that’s not a ridiculously priced NOS part on eBay but since I plan on trying to sell this thing once its fully functional id like it to not be completely made of duct tape if I can help it. 

One of the biggest causes for FAIL, with modded bikes, is the carb jetting, because the builder ditched the stock airbox, and didn't do the homework regarding proper jetting thereafter.

Stock airbox, stock jetting, and you can be 100% confident that the jetting will be correct.  If the bike runs like crap, it's your fault regarding cleaning/assembly, or some mechanical/electrical fault.  

I'm in the camp of keeping things stock.  Do that, get the bike running nicely, and if you want to mod after that, you at least have a baseline, knowing everything is correct to start with.

another potential problem. before buying an airbox. check to see if the ducts are still available. old ducts may not seal properly. nothing is easy on an old motorcycle. ha ha.

ps: on ebbayy I'm only seeing one good/complete airbox but it's for the 440B and probably won't fit. I don't know how easily it could be done.

Here is a link to a fairly cheap airbox that someone fixed. It can gotten pretty cheap and totally worth it. ebay.us/m/jN8EyX   (sorry if I'm not allowed to post links)

that's just the cap. he'd need the airbox housing. there were 2 other caps listed. one broken and one possibly melted/burned.

edit: my mistake. he has the housing.

From what he said, my understanding was that he has part number 11010 and he needs 11012 since he mentioned that he has an area that has two rectangle openings which is where 11012 would go. 

This may or may not be helpful.

If I come up against a NLA part that is way too expensive or just not readily available I will try to fabricate it.

As it pertains to a air box in particular a friend of mine could not find one years ago and made his own out of sheet aluminum. He carved a wood block to fit the frame then used that as a pattern for the aluminum version.

As for the connecting ducts, guys have been using radiator/silicone hose for years to attach drag bike carbs to cylinder heads.

As said above an original air box would be the ideal but there have been a few creative solutions. The link below should describe one such approach. A search here should turn up others

kzrider.com/forum/3-carburetor/599569-cu...x-for-kz440?start=12

Wherever you can stock airbox setup is best for road and everyday riding, now if you are running CV carbs, then stock is the only way to have bike run optimally, other carbs with different boxes,pods or bell mouth, jetting will need adjusting.
i always run stock boxes.

...If I come up against a NLA part that is way too expensive or just not readily available I will try to fabricate it...

along the lines of fabricating an airbox. some of the early kz400s had a fairly simple square airbox that might could be adapted. assuming the carburetor spacing is the same. a block of air filter foam could be stuffed into the box. instead of trying to source the oem air filter. the foam might flow better anyway.

1974 kz400 airbox >> www.partzilla.com/catalog/kawasaki/motor...r-74-75-kz400-kz400d