This is an extraordinarily usefull guide to old sun hardware. The guy who was doing it got overwhelmed with maintaining it, but nonetheless for the older stuff it's an incredible resource.

A compatibility guide to Sun Boards
A connectory glossary
What the LED diagnostic codes mean
Part 1 - table of contents, introduction
Part 2 - guide to the various Sun {1,2,3,4} models
Part 3 - model details, boards
Part 4 - Mbus, 4/6xx details
Part numbers
Various pinouts