The posted schematic is the SSL 242. The '242 is not the older version, rather its the newer. The '02 was the original, and after a while people -notable Hugh Padgam) complained about the fact that when you switched in the EQ -even set flat- the sound changed.
The problem was that when you switched in the EQ, the High and low-pass filters also went into the circuit, (with one very specific exception when you were EQ'ing the monitor path there was an option called "split" that seperated the filters and put them into the head of the channel path, but if you had the EQ in the channel path, it was impossible to bypass the filters also in the channel path... and the High Pass filter's lowest setting was 30Hz, so very low stuff sounded much weaker as soon as you switched the EQ into the channel... not very good by anyone's reckoning!
SSL had realised that there was a problem when the opriginal circuit was designed, and so the half-ass compromise had been to limit the filter slope to 12dB/8ve. (2nd order butterworth). When it became clear that even this was not what people wanted, they commissioned a set of custom pots from clarostat that bypassed the filter when set to the lowest frequency. -They then did what they originally wanted to do and stepped the filter slope up to 18dB/8ve. The low-pass was left untouched, except for the courtesy of having a bypass switch added to the pot (another expensive custom clarostat affair).
Everyone liked the improvement. even then, lots of people still hated the SSL EQ. In 1989 I produced a retrofit Equaliser which replaced either the 82E02 or the 82E242, with a state-variable design, as used in the Calrec, the Neve VR, and the Langley-designed Amek consoles. Such was the distaste for the SSL Equalisers that abother company -Maselec- also made retrofit Equalisers.
Anyhow... if you're making a rackmount version, simply put bypass switches on a '02 and you have a 242, with the only difference being the severity of the slope of the HPF... for as long as that's not engaged, (i.e. most of the time) the rest of the settings will be absolutely identical.
The problem with the 242 is the custom pots... the console uses a 3-gang reverse log with another 100k linear gang, and two switch sections (one a normally closed, one a normally open, wired together in parrallel to make an SPDT changeover) and the switch is in a detent at the counterclockwise end of its travel. That design is a custom from Clarostat, with a minimum order quantity of 10,000 I think, and a likely price tag of about $50 each, -even at that quantity... -That's fine if you're making consoles for a living and the world is buying them as eagerly as they were in the mid-1980's (like SSL for example!) but impossible for a DIY-er to afford.
You can use an '02 design and add seperate toggle or pushbutton switches to bypass the filters, then you have something that still EQ's just the same as a 242.
incidentally, the later 'J' series consoles still use precisely the same circuit when switched to 'E' mode (constant bandwidth, as in the 242 and the 02) as opposed to the 'G' mode (constant Q as in the 'G' series console EQ)
With the exception of the brief dalliance with the 'G' series' original EQ design (the one with the "x3" and divide by 3" midrange switches) the EQ design itself has remained unchanged since the '02. The 242 just added bypass switches and another filter pole (18db instead of 12dB per 8ve). The current EQ still in production is the same, plus the ability to switch all bands between constatnt 'Q' and constant bandwidth... Nobody seems to like the constant bandwidth, so they tend to leave things in the "02/242" 'E' position.
Keith