Remember, the difference between a file and a file with a safe edge is a couple minutes with a belt grinder. I've got three-square files safed on one and two sides, as well as flat and half round files safed in various ways (and let's not get into needle files). Just don't overheat the file while grinding. As a kid, i cut the dovetails in my first flintlock with a file I safed by rubbing it on concrete, and then on an arkansas stone.
I'd try turning the barrel first to align the sight, but if you must. . . . the Mauser factory, ca. 1916, was putting sights on by eye. The action was clamped in a fixture that leveled it, pointed at a vertical line (think plumb bob) in front of a north-facing window. The sights were aligned with the window.
The times I've installed a front sight on a revolver, I did something similar. Pick a surface to use as reference ( on a Blackhawk, I used the left side of the frame (the shooter's left). Level the frame (vertical) and barrel (horizontal). If the barrel tapers, level it off the bore (I've often wondered if a laser in the chamber could be used for this). I use a banded front site, tinned on the inside of the band. The barrel is prepped for soldering before this stage. Align the blade with the vertical reference (plumb bob). Much easier for me than cutting a dovetail by hand and hoping to have it vertical. When shooting shows the sight is where I want it, I sweat it in place. A screw could be used in place of solder.
Honestly, making a banded front sight with files and hacksaw is easier for me than to hand-cut a dovetail on a round barrel and getting it perfect.