It looketh good! Are you still baffling it?
Im thinkin that a baffle that increases some back pressure is a good idea.
I dunno if you guys have played around with jetting.
When I do jap bobbers with 250cc motors I usually swap out the mufflers.
I found that the stock mufflers were too restrictive, but get too close to an open pipe & you lose a lot of power & need to start from scratch with air flow & re-jetting.
But put enough baffling to create some healthy back pressure, & the engine seems to perform better than stock, with no rejetting. Put simply, jap 4 strokes (& I guess their clones) love some back pressure, & rely on a certain amount of it for performance.
Probably telling you stuff you already know but thought it worth mentioning anyway.