Iver Johnson Champion Barrel interchangability

Question
Mr. Gage,

I am the proud owner and shooter of an Iver Johnson Champion 20 gauge.  I received this fine shotgun a couple of years ago as Christmas gift from my daughter.  This gun has renewed my interest in shot gunning which leads to my question.  Did Iver Johnson use the same receivers on the Champion 12 and 20 gauge and should the barrels interchange thereby providing two gauges with one receiver.  Unfortunately, the previous owner of my Johnson "Bubbafied" the barrel with their attempt at magna porting it so I am considering replacing the Barrel and would enjoy the use of a 12 gauge tube.

Answer
Hello, Harry.
 You ask about interchanging barrels from 20 gauge to 12 gauge on the same receiver. What I have found, is that the early Model Champion had a smaller frame for 20 gauge than the 12 gauge. Those will not interchange. However, the later Model Champion had the same size receiver for all gauges. The early model serial number had only numerals, while the later model serial number was followed by a letter or letters. Some replacement parts for the early model 20 and 16 gauges are different than the 12 gauge.
 This is the only information I was able to find. From my experience, I would say they will not interchange. Also, I found that availability for extra barrels are very rare and prices are around $60. The shotguns are available on several web auction sites. Two of these are www.gunbroker.com and www.gunauction,com. for around $125. I would suggest buying one of these in the other calibers.
 I hope this helps answer your questions. Thank you for asking for me. Charles Gage