Oddities Reading boot.img - Way Too Big and Errors In Kernel
It turns out most of the problems seem to have stemmed from my trying to split the boot and recovery images in the wrong place. I was trying to extract the kernel and ramdisk at the 1F8B for gzip (the kernel before, ramdisk after), but there were several instances of 1F8B (specifically 1F8B 0800) in the hex code and the first one was not the correct one.

After splitting the image in the right place, I got a more realistically sized kernel and a ramdisk which extracted successfully.

I was also able to get boot.img and recovery.img via adb from /dev/bootimg and /dev/recovery by explicitly limiting the size as per aureljared's comment on the question regarding my original problem:

dd if=/dev/bootimg of=/where/to/store/it bs=6291456 count=1


Though the images still contain the error messages, I think they're probably supposed to be there as I've found them in some other known good images online.

Note that I haven't truly tested the images are valid as they're just backups and the only way to test them is to flash them and thus potentially brick my phone if they're bad. I'm fairly confident this problem is solved since I can extract the ramdisk, though.