I've recently had to migrate a dated ASA-5505 to a ASA-5508-X. In theory the config should be compatible. In reality a lot of unused stuff has accumulated over the years. And it was deemed a spring-cleaning was in order. So the config was re-created on the new box.
Having both boxes running side-by-side and being able to match the config makes this relatively easy. There was only one thing that had me stumped. Disclaimer: IANACCSE (I Am Not A Cisco Certified Something Enginner)