Here is a list of the ROMs: https://github.com/phhusson/treble_experimentations/wiki/Generic-System-Image-(GSI)-list
There are 3 types of GSI ROMs; arm (32-bit), a64 binder (basically 32-bit with some 64-bit stuff on the kernel side), and arm64 (64-bit).
In order to use a GSI, you will have to reflash stock boot and vendor images first. With stock boot and vendor you can use a64 GSIs. Alternatively you can install my arm64 boot and vendor images from the first post to run an arm64 GSI, but the boot image has to be modified to disable kernel LMK which causes freezes and crashes.