Your in over your head. Take it to a qualified gunsmith.

Unless they are a Smith and Wesson gunsmith they may not have the proper jig for the frame.

Originally Posted by wilburfan

I have a 2 1/2 inch Model 19 (Round Butt) with a non pinned barrel. I bought a used 4 inch Model 19 barrel to have installed. Besides a longer ejector rod what do I need to do to swap out the barrels? Besides proper head spaceing, how big a deal is it to replace the barrel and about how much should I pay a local gunsmith for the work.

Thanks for the help!

I'll try and answer your question,I went through this with a model 66,same gun more or less,but stainless.
It's not something that you'll want to do yourself,unless you have access to a good metal lathe or grinding fixture.The distance from the seat face to the end of the forcing cone is critical,and not something that you can really do with a file.And since yours is not pinned,the barrel is going to be really tight.So,take it to a shop.
If they have the frame wrench,it usually runs in the $80-$100 range.
If they don't have one,and won't get one,go to a different shop.
Bob