Actually, i think most of the BIG systems were pretty much custom, and you'd find individual components from all the major players like Altec, Electrovoice, Gauss, JBL, even Cerwin Vega and Heil/Sunn etc. being used.

Back in the day, manufacturers were fairly generous with cabinet plans. Those "W" bins that you see being used on the bottom end of the RLA-7 system were fairly popular, go fairly low when used in multiples of 2 or more at SPL's that have to be felt to be believed. I think the plans for the ones we built came from EV, but i've seen touring sound companies with the same "W" horns with JBL logo's pasted on them. But, i don't believe any of the big name companies ever produced those cabinets themselves.