I can't really help you with the SCSI messages yet, but I see something else: Unexpected IRQ 3 on device 00000000 This means that there is no handler installed for autovector interrupt level 3. According to arch/m68k/mac/macints.c this could either have been: 1) VIA or RBV macs: unused (?) 2) OSS macs: Nubus interrupt 3) PSC macs: PSC level 3 - slot 0: MACEI have no idea if your Quadra 605 is either of these, or if this list iscomplete. Could you send the output of "cat /proc/interrupts" from your 2.2 kernel?
Certainly - though the same Unexpected IRQ 3 comes up throughout the boot with the earlier working kernels, until klogd starts up. I had this appearing for a while and couldn't find answers on what it was for, and it didn't seem to cause harm, so I changed kernel logging options in /etc/init.d/klogd to KLOGD="-2 -c 4", which hid the messages. The Quadra 605 ran as a webserver for a year, rock solidly.
Here are the interrupts as they appear under the working kernel (2.2.19, not 2.2.20 as I wrote before).
$ cat /proc/interrupts auto 0: 0 spurious int auto 1: 47552 L VIA1 Dispatch auto 2: 8236 L VIA2 Dispatch auto 3: 54 int3 handler auto 4: 0 L SCC Dispatch auto 5: 0 int5 handler auto 6: 0 int6 handler auto 7: 0 L NMI via1 9: 19150 console/cursor via1 10: 1622 adb CUDA interrupt via1 14: 29947 timer via2 17: 47703 F Nubus Dispatch via2 19: 8085 Mac ESP SCSI scc 33: 0 SCC A scc 34: 0 SCC B nbus 61: 151 sonic