With OS 9, the processor specs are noted under Hardware in the Apple System Profiler. (And yes, what refinery said…)
Here’s an “A” board from an 867 MHz QS pictured at the bottom here.
This is a “B” board.
Some other examples… a Dual Processor 800 MHz QS
“B” board noted far left side, near center here - just under that silver screw.
1 GHz Dual Processor?
Label says 1 GHz Dual Processor but that’s a 1.67 GHz G4 Sonnet Crescendo processor (purple heatsink).
Also a “B” board. If you see this purple inside, maybe time to get a little excited.
867 MHz Single Processor
The 867 MHz single processor with an “A” board.
And yes, you can buy “B” boards to replace the A’s. Good luck with that QS. Happy hunting!