I sure hope that your Smith is kind to you on the price as he will correct the issue in about 10 minutes with a sanding drum on a dremel.........
I'm having the the loading channel machined and refinished as well. He's given me a flat rate quote of $125.00 to fit the cylinder, cut the loading channel and refinish the bluing. I think that is very reasonable... since I couldn't do the fitting myself without the right knowledge and experience. It wasn't for lack of trying though. I prefer to do things myself but sometimes you just have to pay the man and move on.