Sounds like he used the 335 first half of the driveshaft then used the m3 second half from the first section to the differential. I'm assuming the M3 subframe places the differential a bit closer to the trans than the 335 which is why it was necessary to shorten it.
Personally I'd prefer to go with a DCT M3 and keep the full M3 driveshaft with an adapter on the transmission side.
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