Thought it would be better to have a separate topic so anyone finding this by search/Google could see it more easily.
I installed four 9-chip, 30-pin 1MB SIMMs into my newly built Plus, and when it boots upon performing its RAM test, I get a Sad Mac code 030ff0. Googling around indicates the first byte (03) indicates a memory failure, and the latter two bytes indicate which chip failed, although since it's a set of SIMMs that isn't a terribly helpful number. I have several sets of this type of RAM laying around and I've tried different combinations and it doesn't work.
Occasionally,