Don’t throw the baby out with the bath water.
Have you re-checked and tested the Ultra-ATA port with a conventional HD?
Might just be an SSD set-up problem OR the B&W having a bit o’ fun with you.
Check it with an
previously working conventional spinner HD alone, first.
Maybe after reviewing this:
http://macos9lives.com/smforum/index.php/topic,6127.msg46280.html#msg46280 Interesting link provided by Ninester in his post above.
(Also the primary reason I left Macs way-back-then too.)
Did your Daystar G4 CPU require any firmware upgrades or
installation of other “enablers”? Which specific Daystar CPU?
You said it yourself that the Rev.2 mobos are hard to find and from what I’ve seen, the Yikes mobo replacement might fit and yield you G4 processor ability in the effort - BUT as far as any performance boost goes - might not actually be worth it - all things considered. You already have the Daystar upgrade. (AND you’d lose the B&W's ADB port.) So hopefully, your ATA is fine and no Yikes mobo will be necessary.
Best of luck.