I was a bit suprised that your focus was to timealign the tweeter with the waveguide - not benefit from the better dispersion?
This speaker has since evolved to a 2-way time aligned passive Harsch XO speaker with good polar dispersion.
Simple Passive Harsch XO Using PTT6.5 and RS28F in a Waveguide
Simple Passive Harsch XO Using PTT6.5 and RS28F in a Waveguide