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.