@Trash80toHP_Mini
The SCSI2SD with zombie hard drive would probably work well for a while, at least until the spindle bearings fail. The only things that would give away the fact that you're using this would be the increased speed and capacity, the lack of the start-up seek sequence, and the thermal recalibration routines like those used on the old Quantum LPS drives.
You could likely program an Arduino to control a zombie drive, initiating seeks off of the SCSI2SD's activity LED, but there would be a few parts required. First you'd need to build a multi-phase motor controller that can maintain constant spindle speed somewhere between 3600 and 5400 RPM, depending on drive model. Most 68k Mac drives operated between 3600 and 4200 RPM, with only high-end drives going up to 5400 RPM. Some AV drives may have spun at 7200, but that speed was more common in the beefier Quadras and Power Macs. Anyway you usually can't just use the original controller board's spindle controller because the drive's main controller often repeatedly cycles and/or completely shuts off the spindle motor if it doesn't POST correctly. Maybe you could isolate the spindle controller from the main controller? It depends on the drive model. Some use that stupid conductive rubber between the PCB and spindle motor, which complicates things.
Anyway, once the spindle motor is sorted, you'd have to program the Arduino to send rapid short voltages to the armature's voice coil to simulate the seeks. Some trial and error would be involved as you figured out the proper voltages and reduce the number of strikes to the limit bumpers. I figure just a constant middle voltage to keep the armature centered and then alternating voltage increase/decrease should be enough to get the clicky seek sound we all know and love.
Synthetic hard drive seeking sounds could be produced through a speaker, which would likely be simpler but you'd lose the spindle sound. I guess you could have the spindle sound on a loop that's interrupted with seek sounds when necessary.