Alright let me try and reply to everything: JB the seat is completely smooth and there isn't any kind of access panel so I'm going to have to cut a hole to gain any kind of access. There are 2 access holes cut into the tunnel further back where I can see the cable sheathing but there's no access to the bracket through those. The frame diagram you posted earlier has the abutment bracket located near the shifter relative fore and aft along the frame. I'll swing by the Home Depot and get a piece of sheetmetal and some u-nuts to make a removable panel. I'll also grab an L-bracket while I'm there and some bolts to fab a new abutment if it's indeed broken. As you instructed me too earlier in the thread when I got the car I took a large screw driver went stab-happy on all I could access and it all seems to be pretty solid though there are some places of considerable surface rust. In short no rot I could find and definitely not rotted the way your frame was!!
Gavin I see what your trying to illustrate but I don't think that's the method for cable tensioning in this particular application. The bracket you highlighted is the assembly that's holding the cable to the pedal and it seems the abutment is behind the interior bodywork. I'll get some well-lit pics here shortly. I'm not worried about originality so much as I am usability. Interestingly the trans isn't the original. It's a gearbox out of an S2. The location of my reverse (all the way right and back) is different from the S1 gearbox (all the way left and back) so i wonder if the cable has been changed before, but probably not. I don't see a reason to change the cable just because the gearbox is being swapped.
Richard I agree with you this was a design oversight for sure! I understand that bracket was welded on the frame and wasn't meant to brake in the car's usable lifetime and not last 55 years but that makes it extremely frustrating to repair!!
I'll have to see if I can borrow a bore scope, but at this point I'm pretty well resigned to the fact that I'll be cutting an access panel either way. I'm going to have to fit a drill into the access hole and make holes for a new bracket if the abutment is, in fact, broken...