I think it's called the TRAC accumulator. If you want your clutch master cylinder on the engine side of the firewall, say good bye to TRAC and ABS. Or create a big headache relocating it.
I did this on a 94. I just plugged the vss connector in to the one on the w58 and my speedo worked fine. Also, not sure if it makes the difference of the world but I used a w58 out of a 93 sc300. And for wiring I only jumpered the neutral safety switch and ran wires to the reverse light switch...