In progress. This is a list of problems I encountered and how I solved them. I figure it can't hurt to be redundant with all the other information. Use the information below at your own risk.
Pop in the boot diskette from RedHat 4.2. Follow the instructions. It will ask you to install the supplemental diskette, and then will give you a very primitive shell with a prompt of the form "#". At this point, mount the correct root partition on some mountpoint like so:
% mount /dev/hda1 /foo
where /dev/hda1 is the correct root partition and /foo is the mountpoint. Change directory (cd) to /foo/etc. Copy the lilo.conf file to a safe place ("cat lilo.conf > lilo.conf.orig"). Now using the old lilo.conf, recreate a new lilo.conf that sets the right partition for the root. Once you are completely satisfied your lilo.conf is okay, issue this command:
% lilo -r /foo
This will install lilo in the right place. Reboot, and everything should work okay.
Replace the milo supplied with RedHat with the one from:
ftp://gatekeeper.dec.com/pub/Digital/Linux-Alpha/Miniloader/latest-Images/AlphaPC164LX/
Create a MS-DOS formatted floppy disk containing milo and linload.exe (supplied with RedHat). Create another ext2-formatted floppy disk containing the pc164.gz kernel from the RedHat distribution (if you have a CD, you can probably boot using the kernel from the CD). Create a third ext2-formatted floppy disk containing the ramdisk supplied by RedHat.
Now, using the Alpha-BIOS, boot from the floppy (see the Alpha Miniloader HOWTO to find out how to do this). This, if everything goes well, should take you to the milo prompt. At this prompt type in:
MILO> boot fd0:pc164.gz root=/dev/fd0 load_ramdisk=1 prompt_ramdisk=1
Alternately, you can just use the CD-ROM if you have one, assuming your CD-ROM device is scd0, and the kernel image is kernels/pc164.gz on the CD, type:
MILO> boot scd0:pc164.gz root=/dev/fd0 load_ramdisk=1 prompt_ramdisk=1
You can use the method illustrated in booting PC164LX above to load the ramdisk. Go through the motions of the install until your CD-ROM (if you have one) is accessed (since it has utilities you may find handy). For RedHat 4.2, the CD-ROM directories can be accessed via /tmp/rhimage in the ramdisk.Pressing alt-F2 (switching the virtual console) should now provide you with a shell prompt. Use it wisely.