Probably some Altec VOTTS, see Analog Addict's system. I once ran across someone using 4 Beveridge Model 3's as surround and was trying to locate a 5th for a center channel.
Ray Kimber used a double pair of nine foot tall Sound Lab Prostat 922s for a couple of years at RMAF to demo his multi-channel recordings. Each pair was driven by a Pass Labs X350.5 amp.
I'm trying to sell my old Sound Lab panels to a guy who wants to put together a 5 channel U-1 system.