To generalize, vertical MTMs will be OK.
I also found a monster thread on avsforum (Monitor Audio Owners Thread) where someone did this with GSLCR. I placed a Wanted Ad here but so far no "used" ones have turned up. Thanks to the dollar's recovery (rather, fall of the stirling), these are now routinely discounted 15-20% (new).
I will start another thread reporting a serendipitous discovery of sorts...