There's a different tooth count on the driven gear depending on the end gear and the W58 and R154 driven gears are NOT interchangeable... The housing for the driven gears on those two are, but the gears are different diameters... I don't know about the A340E though so getting a driven gear matching your end gear from the start is a smart move.
Yes, the short end of the speedo cable should be changed... Some claim you can make it work but I haven't tried it.
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