U24 I think there are two revisions of FDC - The older one, used with the 720K floppy is P8272A, the newer one, used with the 1.44MB floppies is the NEC D765AC. I have two DASD modules, both boards appear identical, have identical P/Ns, but use different FDCs.

   I have a 1.44MB floppy in one (with the 765 FDC),  Uses the 8580 style floppy with the big button below and to the right of the slot. ALPS DFL713A01A, P/N 90X6766

  Hard Drive in my toy is a WD-325M2, MFM for all I can tell.

  The 7552 uses the same U channel drive rails that the 7568 does. The floppy mount is the same (faceplate and rails)