I'm not exactly sure what Amiga Forever includes, but the Kickstart files used by the A3000 aren't just plain ROM images - they also include what's known as the "bonus code" to initialize parts of the A3000 hardware (which makes them slightly larger than 512K). Normal ROM grabbing tools can't pick up this bonus code, so you need to get one off a SuperKickstart disk.
If Amiga Forever has these special ROMs, then you're all set. Just remember that the file has to be named DEVS:Kickstart on partition WB_2.x: (slightly annoying with Kickstart 3.1 for the lightly neurotic among us ;-))
