Hi fpmurphy.
Trying my old "sun.com" links I was redirected to the site "download.oracle.com/docs" where I found "Servers, Systems Management, Workstations, and Related Hardware" then "Legacy Sun Workstations"; there I found "SPARCstation 20 Workstation" link pointing to related docs: only one document, exactly the same you found and suggest. Now I think it's impossible that for the SPARCstation 20 exists only one official document!
The old_but_good site sunshack.org is pointing to at least a couple of docs more about this machine (but the links are "sun.com") and the info they are presenting is incomplete (as they state).
I tried to search by Google for more docs (for more specific docs too) but I was unable to find any of useful.
The same is valid for Javastation 1.
Instead about the SunPC coprocessors the things are different, worst I mean: support files (fixes) for old Solaris versions (9, 8, 7 or earlier) are protected by a request of login. No problem: I was a registered user of Sun... Wrong!
When I access with my "sun.com" credentials they are asking for a valid contract number, without it you cannot continue.
I contacted the Oracle support team for a "small" quotation for a contract (I'm a private not a company): they told me that I must be a company!!!
So... Help!