That strange whirring sound you hear in the distance?
It's Samuel Colt and Captain Walker turning over in their graves at about 2,000 RPM at the thought of putting a laser sight on the 1847 Walker!
As far as cap and ball revolvers go: live with the sight disparity.
If you MUST have a revolver with adjustable sights, buy one of those Remingtons with modern sights, or a Ruger Old Army with adjustable sights.
But I dislike snobs so I won't completely be one about your Walker.
Every Colt cap and ball revolver I've encountered shot high. To remedy this, you need a taller front sight.
An enterprising gunsmith, familiar with such arms, could fashion a tall front sight from brass, German silver, pewter or iron. It should be overly tall, so even the most powerful load shoots low at a pre-determined distance (presumably, 25 or 50 yards).
Then, once you've found the ideal load, and settled on it as the one load you want to stick with, begin filing down that front sight a lick at a time.
Eventually, you'll reach a point where the sight picture coincides with the bullet impact.
I would suggest that you have the sight fashioned in a half-moon shape, instead of a post sticking straight up. A half-moon sight will be less apt to break and not tear the leather inside your holster. It will also look somewhat more authentic.
But as for a totally adjustable sight on a Walker? I know of no such animal that wouldn't look like a monstrosity.
Putting modern, adjustable sights on a Walker would be an affront to a fine, historical arm. It would be like painting a Dusenberg with a can of Krylon spray paint! :eek: