I think that, currently, you should focus on the hardware side of the issue, more than on which tool(s) might be able to read the disk. You need to find a way to make an old Mac-formatted internal SCSI drive work to be able to access its data. If you haven't got a PC that can support that kind of SCSI drive, if you haven't got another vintage Macintosh that could access that drive (either internally or externally via a SCSI enclosure properly terminated), then probably trying to fix the LC475 itself is the easiest path.

On that matter, I tend to agree with register -- if the 475 was working perfectly when it was put away, it seems unlikely that the power supply is at fault; the battery, drained out, might actually be the prime suspect. But then again, in almost 20 years of Mac experience, I've seen things which are closer to Black Magick than Computer Science

Cheers

Rick