I have an H&R Model 058 (It does not say "Topper", just Model 058) which, according to it's AZ prefix serial number, was made in 1985. I bought it used with a 20 gauge barrel and a 30-30 barrel.
I have since seen several other combos, some marked "Topper Model 158", in both blue and stainless (with a BA SN prefix) and have been informed that there were numerous combos of 2, 3 and even 4 barrels on these guns. Calibers were 30-30, 22 Jet, .22 Hornet, 20 gauge, and 12 gauge. Possibly more.
I am under the impression that the Model 88 Topper shotgun was the same frame and receiver as the Model 158 which I know came with combination rifle barrels. So, I don't think it would be a safety issue to use the 30-30 barrel on a pre 1986 cast iron frame PROVIDED it fits, locks up, and is fitted correctly. And, that the cast iron frame it's going on is in good, usable condition.
I have also been specifically told that the older barrels will not fit the newer SB1 and SB2 frames but do not know what exactly is stopping them from fitting. It would seem to me that the newer frames being stronger should accept the older frames safely so it must be some mechanical issue, not a safety issue.
Dan R