You should start here: http://lowendmac.com/lisa/lisa2.shtml

It says: "...the Lisa 2 adopted the same 400 KB 3.5" floppy drive as the simultaneously introduced Macintosh." Maybe you can fit a 400k drive in the chassis?

Hard drive replacement - look at these guys, who built a compact flash drive to replace the ProFile: http://sigmasevensystems.com/xprofile