Attach the SSD to the new Qubes installation.
Open a disposable, and ensure it has adequate space for the purpose: I
suggest you make it offline.
Attach the relevant volume to the disposable, using qvm-block attach
Decrypt the partition containing the old Qubes install.
Mount the Qubes partition in the disposable.
Find the private volume for the standalone (under /dev/qubes_dom0)
Mount that volume.
Identify the files you want.
Either copy them to a directory in the disposable, and qvm-copy that
directory, or qvm-copy them directly to the qube where they will be
used.
It takes longer to read these instructions than to get this set up.
I never presume to speak for the Qubes team.
When I comment in the Forum I speak for myself.