@elliottbnewcombjr Nice piece! Take another look at that front panel.
The EQ curves were very much standard by then. 'NAB' is a tape equalization. RIAA and the 'RCA Orthophonic' curves were pretty much the same thing; RIAA being for stereo. AES and LP were two alternate mono-only curves and the '78' curve was an approximation of the most common 78 curves of which there were quite a few.