First: This is not a custom gun by some famous builder, like our Mike Brooks, or Roy Stroh. Its not going to hold any real value by the time you sell it. If you wait for the inflation to increase some more, you may up receiving more "cash " than you paid for the gun, but that cash will buy less then, too. So, don't be so darn worried about any changes you make to the gun. The people in the market for any used gun are interested in a gun that works, costs them less than a new one, and has had the bugs worked out of it. If you change that front sight to make it easier for you to see, than the factory one, the buyer is likely to consider that an asset- not a loss for choosing to buy your gun vs. an "original".
Now, having said that, call any supplier, and they can fix you up with a new front sight with the correct sized dovetail. Only the folks at Dixie Gun Works, in the distant past, have shown an indifference to customer service, in my personal experience- so Often I stopped buying from them.
I suspect that is why we have so many Other suppliers these days. And, I hope Dixie has changed how it deals with customers over the phone. They almost had to change, or they wouldn't be in business any longer. The number of complaining customers were legions! NO company can stay in business very long with so many unhappy customers telling all their friends to find another supplier.