My Raspberry Pi 4 aarch64 repo

[keithspg]

I am a bit of a noob, but have experience building packages and stuff for RPIB1/B2/3 (armv6/v7). I do not have a Pi4, but do have some Pi3s and am interested in playing with the 64 bit stuff. I d/l and installed Arch_Latest for aarch64 Pi3B+ and I get no RPI overlays. I tried building a kernel by modifying the linux-aarch64 PKGBUILD/files with info from the linux-raspberrypi4 PKGBUILD/files and get a non-booting system. It gets close, but does not boot. I get past the rainbow, but it cannot seem to see the ethernet port:
$this->bbcode_second_pass_code('', 'Net: No Ethernet Found.
starting USB
...
found U-Boot script /boot.scr
708 bytes...
...
SCRIPT FAILED: continuing...
...')
I was looking at moonman's PKGBUILDs and have a couple questions.
Do I need to change the 'buildarch=12' to 'buildarch=8' to get a working kernel on my Pi3 from moonman's archive? Is there one image which will boot on both architectures (like armv7 on Pi2/3/4) or is it a new image for each one?
Can I install this on top of the image I am running as a downgrade? I am running an image made from ArchLinuxARM-rpi-3-latest.tar.gz which is running 5.7.1-1, I think.
Do I get overlay capability? i.e can I put dtoverlay=xx in the config.txt and actually get the device to be recognized?

Regards,

Keith