The problem with that operating range is that it includes the HD-20 which was essentially the same mechanism used in the HD SC. And pre-'85 there wasn't much, particularly in the 3.5" arena.

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Thinking about it, there were quite a few third party hard drives for compact Macs that used a vertically mounted mechanism. eg MicahDrive AT (an internal solution) and SuperMac externals. And Macs like the IIcx and IIci were designed to operate in either orientation.

Come-on Charlieman what's the worst that could happen? I have read that the earlier drives must be formatted in whatever position the drive is to be operated,however.

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Remember that hard disk drives are mechanical devices. Changing the orientation may cause additional wear on bearings or the disk head mech. The worst that can happen is a head crash and total loss of the disk. However the change may be beneficial, distributing wear and increasing disk life. Unfortunately the only way to test is to do it.

I too have read that the oldest disks should be low level formatted in the orientation in which the are to be used. My understanding is that during disk verification, the formatter has to predict future defects which may differ according to disk orientation.