These are awesome, best found old/used (meh on the new ones) 
Discussion
Picture from the internet, not the pair I restored.
Long fun history, legend says they were used in JFKs campaign tour. They work on any from and can be stacked as sound wall. Sound absolutely fantastic.
They're impressive! And interesting history, might suit my set up as I don't currently have a bass unit, just read they have a good crossover range. I'm going to see what's about 2nd hand like you said, thanks!