Hi Greg,
mmmm, dunno about using the B for lum (a great deal of the wave lengths are filtered out).. While it looks ok, it has sort of muted the potential I think.
Why not discard the B and use a desaturated/ mono version of your combined RGB, there's 120' worth there. do some extra contrast, sharpening... whatever works and recombine the Ha data to it and see how that looks, then re combine to the RGB data.
God, you gotta hate it when you have the wrong filter slotted
All the best
Rich