Yes it will. All the 1200 will use the 1300 barrel and here is an excellent source for barrels. http://www.midwestgunworks.com/merchant2/merchant.mvc?Screen=CTGY&Category_Code=winchester-model-1300-barrels
Model 1300 barrels will fit the 120 and most 1200 barrels as well. Except that a large amount of 1200 barrels are made for 2 3/4 inch shells only. So you have to be careful which 1200 barrel you would purchase. Because the 120 is capable of 2 3/4 inch as well as the 3 inch shells same as the 1300 models all were.
Try a 1300 barrel
The only barrels that will fit the Winchester model 120 are all model 1300 winchester barrels,and most model1200 Winchester barrels.So the answer to your question is No.
I recently called the Winchester historian and he said they were the same gun also a model 1200 barrel will fit.
no the 1300 barrel does not have gas ports in it yes the 1300 barrel will fit ,no it does not have the gas ports BUT any competent machine shop or gunsmith can drill out the ports for you.
any 1200 or 1300 will fit the ranger 120