If it is ever 1977 again, I'm going to use these amps. My son found them at a nearby house with a 'help yourself' sign next to them. It would have been rude not to take them!
Recording Studio Design later became Studiomaster. The model number of this amplifier is 800b which implies 800 watts which I also assume is 400w per side, Each amplifier's heatsink has eight 2N3773 transistors so it is feasible.
I haven't found out much about them other than something about the company wanting to bring the high quality of studio recording to live sound.
Speaker outputs on male XLR. Input unbalanced on XLR. Power input is also on XLR (but a version intended for high voltage) There is a big fan on the back but if they are rack mounted, gaps will need to be left above and below as the only other ventilation is in the top and bottom panels.