I'd ask if he's just got the tranny or if it includes the clutch and flywheel.... make sure it comes with the bell housing as well. A clutch master cylinder is dirt cheap from most parts stores (up to maybe $50). You only need the bottom half of the speedo cable which runs about $15 (NEW)... you do NOT need to replace the top half, and personally, I'd see if Your current speedo cable is long enough to reach without even replacing the bottom half (the auto's lower cable is a different length and it has a 90? bend in it where the W58's is straight and curves across the top of the exhaust before running up the firewall).

W58s are generally inexpensive as they aren't as robust as the R154... so it's a popular swap. But find out as much as you can before buying the tranny (mainly if it was used in hard launches or used on a turbo'd MKIII), you want to be sure it's in decent shape before you go to the trouble of installing it.