To mount the HF horn I would use a "T" shaped platform attached to the front/top of the horn in-line with the original dimensions, supported by the triangular brace. A similar method below to support the mid on the bass unit. Still all a bit academic at the moment as these are just ideas in my head and on the doodle pad!Don't remember any posts about altering crossover points TBH, the end result with mine is impressively cohesive as it stands - I certainly can't hear the joins ;¬)
Paul