The pre lci flywheel setup is different. The pilot bearing is the crank pre lci, post lci it's pressed into the flywheel. Pre lci is e39 post is more like e46. The input shafts are splined different I think. It's the same engine block and chassis cross member, so I guess it would probably work if you change the whole clutch and flywheel.

26 mpg .., wow. I'm at 19 and thought it was healthy. 80-85 is where it likes to cruise. I don't think I could get close 26 though.

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'05 E53 3.0 6mt
'17 F30 340ix 6mt
'96 E36 328is, in progress