Sean,
I assume this M40 is off a 140? The 140 flange seems to be a lot larger on the M40. I don't know why they did this, because the large flange ALWAYS cuts into the silly plastic covering under the shift linkage.

I should really document the differences while I have all this stuff sitting on a shelf next to each other.

8.5mm isn't very much. I would see if it bolts up. The center driveshaft "coupling" has some play in it and can slide back and forth. I would loosen the rubber mount (not remove) and see if it'll fit in.

Reason I say this, the 140 overdrive driveshaft halves are the same length as the 122 or 1800. I've had them benched together and they are nearly indistinguishable, though flange variations do exist. That tells me the distance between the engine and center driveshaft bearing are likely, nearly the same.

Jim
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cars trucks and volvos