Seems the "search" function here has a limited scope. I went back to 2001 to see if there was any info on identifying this odd clutch pedal. A poster, "wongg" in 2002 referred to Ross Converse saying that there were two different pedals used on 200s and elsewhere some one thought that the 260 diesels used a cable clutch. I'd thought that ALL diesels used hydraulic. Maybe that's what this thing is? 260 diesel?
Also, way back then there were postings of the "T" end of the cable breaking off. The new, unused cable I have has this "T" on the upper end and the plastic Volvo adjuster and a ball on the lower end. It appears to be a pretty stout item. Better to use this cable with the "T" and the corresponding pedal? Or the '83 242 Turbo item with the clevis/pin?
Next step, I guess, is to compare this style cable to clevis end cable to see which is stouter and available when replacement needed.
On that "diamond" shaped plate with the vacuum line running through it; This other pedal, (for now assuming it may be a 260 diesel item), shows no sign of bolts ever being in the weld nuts, no marks from mounting the plate, looks never used.
Drilling the hole in the firewall plate for the grommet and cable as shown on page 410-2 in the Bentley book looks fiddly, but do-able.
Photo, "Fig 3" on same page shows clevis/pin attachment with the caption, "Early cars use clevis pin and cotter pin (arrow) as shown. Later cars use bolt and locking clip". But I can't find a photo of this.