It's so funny you would say that about adapted motors, because the Astro Jr. is nearly identical profile to the Astron, same dia., length, NC and fins. The differences are the Astro Jr. came out first, has surface mount fins, 13 mm mount and parachute. I think when the Astron was released it functionally replaced the Astro Jr., since it could be adapted down.
This is the big problem I'm seeing with online vs the old catalog formats. It's a real dive to find out details, what makes them special and how they related to others.