I had four of those 115SR cabinets with two Coliseum Large Radial Horns with my Sunn Coliseum PA back in 1975. Awesome sound system in its day. I had a Coliseum Audio Control (8 ch) mixer, a Coliseum slave for the cabinets, one concert slave for the horns and another concert slave for the four monitor cabinets -- two small guys with a 12 in each cab as monitors for the drummer and B3 guy, and two 410SR cabs the we used for side monitors to shoot down the front line. All of it came from Metro Music in Atlanta, along with some other Sunn gear, a Wurlitzer electronic piano and a good size wall of Fender amps.
Sure would love to find some of those 115SRs for "cheap," but I already have more gear than I'll ever need - really!
Warmest...