H & R can I swap barrels safely 20 ga. single shot

[chrisbob]

I seen an old H & R topper jr model 490 20 gauge ?? 1964 ?? I don't believe the stock and everything is original to the barrel. It was only 50 bucks for sale. But can I find a 12 gauge barrel that will fit safely or find any info on the serial # to know if the barrel is original the the rest of the gun any info is greatly appreciated thanx?

 

[sm]

http://www.hr1871.com/Support/accessoryProgram.aspx

 

[Chawbaccer]

The whole gun only costs about 90 bucks brand new.