Let us know how the conversion goes and how you attached the plate, etc (pictures would be great).
My first thought about the low-rev "blurrb" is that it's just running rich on the needle straight section or something, especially seeing as you've had to go leaner on the idle circuit. I doubt that the divider plate will fix this, but I don't really know what effect it will have on jetting.
Anyway, go for it, but if the "blurrb" is still there, try leaning off the jetting on your needle straight section.
Good luck.