Rob:
While the sight could be fit by measuring the two dovetails with rolls and doing the math, it is not really necessary.
I assume your new sight is close to the correct size. Pick one side of the dovetail on the sight and file it at a very slight angle so as to make it tighter as it goes in. You really don't need the wedging angle, but ever so slight of one will prevent the opposite angle, where it gets looser as it goes in.
You can use a magic marker to color the metal as you file, to be sure that you are cutting where you wish to. Just go slowly and carefully until the sight will start into the dovetail on the barrel. Reinking with the marker will show where the interference is. Take another stroke of the file and try again.
Ultimately you want it to tap into place. The key is to find the happy place between a beat it in fit and a slide it though and fall out the other side fit. It is not difficult if you are patient.
Best of luck.
Glenn
