8" drive variations

As hinted at in another post a few days ago, I'd like to add an 8" drive (or possibly more than one if necessary) to my Imagedisk machine in order to be able to archive 8" media. My knowledge of 8" drives is practically non-existent, so what are the gotchas involved? Things like: Do 8" drives exist in both hard and soft sector variants? Is one far more common than the other (as with 5.25")? Do 8" drives exist with wildly different track counts (40, 77, 80 etc.) and again is any one particular flavour far more common than the others? Are there any problems with some particular drives that'll make interfacing them to a '765 type FDC more difficult? etc. etc. I suppose the real big question is: Is there a particular flavour (i.e. geometry and interface, not specific brand) of 8" drive I could use that will mean that I can read and write the majority of 8" floppies found in vintage hardware? That would at least seem like a good initial step, and I could worry about the minority formats later on. cheers Jules