According to Porsche Parts catalogue, both side bearings (taper roller bearing) are the same size (well, at least on the long bellhousing 930, not sure about the short bellhousing 930)
Then don't order off that catalogue. The OD of the bearing that takes the thrust (i.e. the one in the sideplate) is 90mm, the one on the non thrust side (i.e. in the trans housing) is 80mm and that's the same for both short and long bell. I've got both here.
930 case is made of aluminium, not magnesium. You know, hewland DG300s have removable side plate on both sides.
Not sure how you see that info being relevant? The side plates are the strong bits on both trans. Have you seen how strong the Hewland side plates are? They are beefy.
Standard practice for a big cube motor coupled to a 930 is to fit a stronger billet sideplate to take the extra side thrust generated by the higher torque. You can't easily beef up the trans housing where the (smaller) bearing sits if you make that the thrust side by flipping the ring gear.
Please cite your source.