I'm wondering whether picking up a solitary 910A as and when it appears, rather than waiting for a pair might be a good alternative approach? 😊
On a completely separate note, and just thinking aloud (!): would it make any sense to try using a 12" PA speaker on the floor or if we have one going spare (or even better, your 745A!) and just use for low bass and kickdrum with crossover set at (say) 120Hz, plus HPF maybe at 30Hz, and then let your tops just deal with everything above 120Hz?
I suspect you would get a bigger sound than just your two 310A tops, and not have the weight of a heavy sub to deal with? What do you reckon?