man your stubborn 
i suspect that the cpu has a broken mmu or fpu,or the board was never intended to run 66mhz(thats not the original cpu it came with) or the its the hokey xtal soldering.more than likely the 66mhz overclocking is screwing with the scsi chip.these are all guesses,but easy to eliminate each.
RAM may be unstable at 66Mhz too. Use 50Mhz. Or 56Mhz if you like, but not more.
