I'm not very familiar with Macintosh, so my answer is based on my general knowledge of the Motorola 68K architecture (like the 68020 that the Mac-II is based on).
In the Repair and Upgrade guide (page 197), the ROMs are refered to as
U3: Low ROM
U4: Medium Low ROM
U5: Medium High ROM
U6: High ROM
As the Mac-II is a 32-bit "big-endian" ...
Linux has native HFS read/write support. Most distributions do not include it by default, but if you install hfsprogs and the kernel modules, you should be able to mount the disk, or an image of it, like a regular file system.
Dealing with the resource fork, however, is a bit complicated that way, so you can't expect applications and such to work if just ...
It sounds like you've done what would be immediately logical, but are misunderstanding some concepts to diagnose the problem. If could be that the HFS code in the kernel is no-longer working, but its more likely there is a problem with your disk, or the permissions needed to access it.
So apologies if this is too basic but.. Firstly the whole disk, is ...