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The cable attaches to a small lever inside the transmission. I believe you can access this connection by simply removing the transmission pan. Search the archives; I recall someone posting pictures many years ago
Doug is correct; not a hard job on a BW66. I've done it. Yes, have to remove the pan. And the adjustment after assembly is pretty ticklish without a pressure gauge. But you can get it correct with patience. I would replace the transmission filter and gasket while you are at it.
The S2 would have a 65 gearbox, with similar cable operation, but as it has carbs, it pulls from the linkage, whereas the S3's 66's pull from the throttle.