I have a Topper 158 16 ga. that was my first gun. I got it for Christmas roughly 30 years ago. It has an AJ206XXX serial number. The barrel does not have the last three digits etched/scribed on the lug like my NN serial Handi.
Also, my Handi barrels (.223, .44, .243, and 12 ga.) will all lock up tight on the Topper frame. My 16 ga. barrel from the Topper will NOT lock on the Handi. I would consider shooting the 12 on the Topper, but nothing else. An old Topper barrel would be cool in 30-30 though.