I also have a Model 058, doesn't even say "Topper", just Model 058, that came with a 30-30 barrel and a 3"-20 gauge barrel. My serial number is "AZ", making it a 1985, I suspect they made the 1986 year start with a "B" to avoid repeating. Since "AA" was already used in 1964, "BA" was used for 1986. I have seen others with a "BA" prefix. The last one I saw was a pretty nice shape 30-30 and 20 ga combo in stainless (?) and wood that I saw at a LGS, he was asking around $275 for the combo
I don't think the .357 Maxi was standard to the Model 058, although I am pretty sure the 357 Mag was. My research has also turned up 22 Hornet, 30-30, 22 Rem Jet, 20 gauge, .410 gauge, and 16 gauge in the multi barrel combos from H&R before they folded.
Maine1, if you want to get rid of that .357 barrel I could give it a good home. PM me if you have any interest in letting it go
Regards
Dan R