OS doesn't see the partitions after reboot

[dt]

I have tried to install GuixSD on my non-UEFI PC from USB and I have
encountered multiple problems.

1) The USB is /dev/sda while HDD is /dev/sdb during the installation,
but after reboot HDD becomes /dev/sda.
How do I set the device for the bootloader and swap partition without
using device tree name (/dev/sdX)?

2) I have set the labels on HDD partitions this way:
/dev/sdb1 (ext4) - boot
/dev/sdb2 (ext4) - root
/dev/sdb3 (swap) - swap
/dev/sdb4 (ext4) - home

The config file for my system is attached.

After invoking `guix system init /mnt/etc/config.scm /mnt` and rebooting
the OS fails to mount the partitions because it doesn't detect them.

config.scm
Description: Text Data

signature.asc
Description: OpenPGP digital signature