[Hellgate]

At 75 feet, 2" high & 2" right is pretty darned good. If you were daring, you could cut the notch a little over to the left a bit. The formula for correction is:
Correction X is to the sight radius as 2.5" is to 900 inches (distance to target). If your sight radius is 10" then the equation to solve is X/10=2.5/900
X=25/900 which is .028" correction to "move" the rear sight over. I.E. you could file/cut/dremel the rear notch so its center is moved over about .03" to bring it to zero off windage wise.

Before touching the sights I would shoot it more with different loads and maybe even different ball sizes like .451 or .457 and 20 & 30 gr powder charges. Also shooting the gun a bit might make it settle in to where the POI might shift a bit. I would be happy with that lille windage being off at that distance. Also shooting the gun from a rest vs two handed vs one handed will make a big difference where it hits so try different holds before messing with the sights.

Most of my Colt style C&Bs have the rear notch deepened a bit and widened or tweaked to one side a bit from how they came from the factory. Deepening the notch will also lower the POI. If a gun is shooting very high you can grind down the hammer tip to lower the rear sight and recut the notch.