Kernel Panics, Gray screen of death, and hard drives, oh my!

Question

Last week, while performing multiple tasks on my G4, Safari froze up and completely locked up the entire computer. I rebooted by manually pushing the glowing power button the front of the tower. During reboot, I got the gray screen of death with the "you need to restart your macintosh... by holding down the power button for several seconds" message.
After a couple tries and getting that exact same gray screen of death, I started to worry about all my data.
I took both drives out of the G4 Quicksilver - one, a 500gb Barracuda Seagate (Master/bay 1), the other a 200gb Hitachi (slave/bay 2). I hooked them up to an older G4 and ran DiskWarrior and DiskUtility on both of them. The master drive had serious (>34%) fragmentation, which has since been cleaned up. The slave drive was relatively fine.
here's my current problem:
When I hook up:
1. Just the Master with no jumper pins, the drive runs fine, no problems, all settings and prefs are there, etc.
2. Just the Master with the correct pin settings, I get the kernel panic screen of death
3. The Master with correct pin settings and Slave with correct pin settings, kernel panic screen of death
4. If I swap the Master and Slave, and make the correct pin settings, the booting process starts and then I get a light gray screen with the "ghostbusters/do not enter" circle.
I put the original Slave drive in an external HD firewire enclosure, and it will mount on the desktop after the original Master drive has booted up - BUT - if I have the external drive powered up before I boot the Master, I get a gray screen with nothing on it - no message, nothing but grayscreen.
I've backed up my critical data, but would like to get these two drives back into their normal operating Master/Slave relationship that served them well for the last couple years.
Any help greatly appreciated.

Answer 1

New wrinkle:
This morning trying at boot up, the Mac chime sounded, the gray screen w/the apple logo appeared, and then the machine sounded like either the main fan or one of the two drives spun down. Shortly thereafter, I got the prohibitory sign again.
I rebooted and then got something completely different: a black screen with a small blinking vertical rectangle in the top left of the screen, with nothing else happening for a long time, so I manually rebooted and tried to boot into safe mode.
Trying to boot into safe mode gave me the chime, the apple logo, and then the sound of either the fan or drive spinning down and leaving me at the prohibitory sign once again.
Finally I option-booted to the slave drive and upon startup, received the following crash report, which might as well be in Swahili as far as my being able to make sense of it:
Sat Apr 11 09:59:48 2009
Unresolved kernel trap(cpu 0): 0x300 - Data access DAR=0x0000000003DFFF70 PC=0x000000000032F68C
Latest crash info for cpu 0:
Exception state (sv=0x2d409780)
PC=0x0032F68C; MSR=0x00009030; DAR=0x03DFFF70; DSISR=0x40000000; LR=0x00287A40; R1=0x2D3BFDD0; XCP=0x0000000C (0x300 - Data access)
Backtrace:
0x2D3BFE20 0x00287AA0 0x00288658 0x0030C5AC 0x000B34C8 0xFFFFDFFF
Proceeding back via exception chain:
Exception state (sv=0x2d409780)
previously dumped as "Latest" state. skipping...
Exception state (sv=0x24459500)
PC=0x93091180; MSR=0x0000D930; DAR=0x00100AE4; DSISR=0x40000000; LR=0x000067FC; R1=0xBFFFED50; XCP=0x00000030 (0xC00 - System call)
BSD process name corresponding to current thread: launchd
Mac OS version:
9G55
Kernel version:
Darwin Kernel Version 9.6.0: Mon Nov 24 17:39:01 PST 2008; root:xnu-1228.9.59~1/RELEASE_PPC
System model name: PowerMac3,5
panic(cpu 0 caller 0xFFFF0003): 0x300 - Data access
Latest stack backtrace for cpu 0:
Backtrace:
0x0009BCF0 0x0009C694 0x00029EA0 0x000AFA90 0x000B32F8
Proceeding back via exception chain:
Exception state (sv=0x2d409780)
PC=0x0032F68C; MSR=0x00009030; DAR=0x03DFFF70; DSISR=0x40000000; LR=0x00287A40; R1=0x2D3BFDD0; XCP=0x0000000C (0x300 - Data access)
Backtrace:
0x2D3BFE20 0x00287AA0 0x00288658 0x0030C5AC 0x000B34C8 0xFFFFDFFF
Exception state (sv=0x24459500)
PC=0x93091180; MSR=0x0000D930; DAR=0x00100AE4; DSISR=0x40000000; LR=0x000067FC; R1=0xBFFFED50; XCP=0x00000030 (0xC00 - System call)
BSD process name corresponding to current thread: launchd