yard man lawn tractor

I bought a Yard Man model 131-684f595 it is 12.5 hp.
It had a v-twin in it , I assumed it was a replacement motor maybe 17hp or so.
I was looking for a motor to replace a craftsman 12 hp single.
I looked up the model number 290777-0107-01 and to my surprise it was a Vanguard 12.5 v-twin. It must be the original engine. I didn't know they made twins that small. I only wanted the engine but had to buy the whole tractor.
It's some sort of 7 speed automatic. I will probably trip it down for parts.
Its missing the air cleaner cover that I didn't notice was missing.

Nice little engine. Yeah, 12 or 12.5 were the smallest twins I have seen.

Nice score! I was excited when I found a 14hp Vanguard twin, more torque! Lol. In all honesty that's a great little engine, especially great because it's pressure lubed, its hard to beat the Vanguards in my opinion

Am I just missing the air box cover. I have taken a few parts off to blow out the leaves.
I tried looking online for a cover for that model and I get different results.
Some round filter, clamp on square cover . I looked at some pictures so I think I know what it looks like but can't find it .
What I the piece of metal cover the carb intake for?
Could I just take the air box off and make an adapter to use a round type filter that just clamps to the carb?
I have a mill and a lathe.
I don't what to spend more on air filter parts that I paid for the tractor.

Briggs and Stratton part # 805359. I had a quick look on eBay but didn't see one.

Sure you could make a tubular intake what's important is to match the size of the carburetors intake "mouth". Might as well make it a snorkel while you're at it which gives the added benefit of a longer tube which is good for extra torque. Some fellas have successfully made them from plumbing PVC.