My DIY ribbon is similiar: a DIY ribbon of 48 inches with four 7 inch PE ES-180 woofers next to it crossed at 825 Hz. Vertical woofer spacing is 11 inches, ctc. Works fine. I can't find any evidence of comb filter problems.

Overall this speaker compares very favourably to my Eminent Technology LFT-VI which is a full 6 foot line source (although its ribbon tweeter is less than the full height).

The strictest guideline is ctc should be less than one-half a wavelength at all frequencies that overlap. I'm using a 4th order Linkwitz-Riley crossover (active) to minimize overlap. What type of crossover are you planning on using?