On some of the old bikes (50s?) the little oval box was the air cleaner. I think you could come up with a way to do it, but I think the air hose approaching the throttle bod would not have a straight run. Some of these bikes have been shown to be sensitive to getting rid of that hose. I put a cone filter right on the TB and dropped 10% from my MPG.
If you're inclined to try it, I'd get a cone filter and try that. Or you could run a length of radiator hose from the TB and under the seat to the left side of the bike to smooth the flow. Someone did that. Another option would be to simply get an ACE air canister. A few have been installed on UCEs with good result.
If you're dead set on converting the oval tool box I'll bet you can. Might need to be a bit creative is all.
Scott