FWIW, I ultimately sold my 210s because I could never completely ameliorate its parallel wall distortion without resorting to a ~300 Hz/2nd order XO [its original design alignment], so theoretically it takes a 600 Hz/4th for the small parallel wall horns or higher order if a higher XO point is desired and why I cut down 825 cabs way back when. All things considered then, it's still the best option if a pair can be located locally for what it would cost in materials to make + however much you're willing to add to keep from having to construct the flares.

GM