For `sun4c` kernel architectures (most SPARCs before multiprocessing), I'd try to get the source for 4.1.4. At least some of the older Sun-3 might need an older version, and I recall our Sun-386i systems were stuck at 4.0.x.
Then, unsurprisingly, the old Quantum SCSI disk was only happy enough to make grinding noises and no more. I found a guy making SATA to SCSI adapters meant for these old Suns and paired that to an SSD I had lying around. Hey, look, that now works too.
Finally, by setting up tftp, bootp, and NFS on a FreeBSD VM I was able to net boot the machine and install SunOS 4. My goodness, I had forgotten how slow the thing is, and how much has changed since the 1990s. I was able to get a bunch of more modern stuff to compile, but it was a fight every time.
Next I was going to drag out the old SGI Indigo, but haven't found the energy yet.
I'd be curious if you find a trove of the random open source SunView software from that era. A later SunSite mirror still up is at http://sunsite.informatik.rwth-aachen.de/cgi-bin/ftp.new/ftp... Starting from a Usenet archive, to find the names and original FTP sites of software might help. (Especially programs circa 1990 with names ending in "Tool". There was even a ToolTool.)
There's also commercial software. FrameMaker and Interleaf at the time were arguably nicer than 2022 Microsoft Word, for example.
https://www.sunmanagers.org/1992/0383.html
There were various remedies, including slapping the drive, and dropping it flat onto a desk a very short distance.