Is your centrifugal clutch stock? The one pictured by the retailer has a bit of a conical shape that adds about an inch to the overall width of the transmission. See the round "detail" picture in the upper left.
Here is a picture from a different retailer.
The thing that confuses me is that yours is completely flush. Did you specifically ask for the flush version, or is that what is sold nowadays? Like I said, I really like your setup. I want to make sure I can get the same parts.
And how do you like running without the engager? I always disengage the drive when I stop to reduce wear-and-tear on the clutch. Has your centrifugal clutch suffered by always being "on"?