The speedo drive is electronic on the 717.402. It also came with the w126 euro as an option I believe. 717.401 has the starter on the left. They are all the Getrag GL275. 717.400 401 402 404 420 421 422are the ones I've seen that have all the same internals for the most part. The 404 is the dogleg but its mostly the same . Torque input rating is 270Nm for all of them, but Ive read of them taking much more.More than 400nm I have read in some cases.

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Chris
84 280sl
82 300d euro