All these guns may have been sighted for a bottom of the bullseye, probably using 148g HBWC or 158 SWC. Since you are probably not shooting in competition with that revolver, I would simply hold a foot low and keep shooting. Remember that this generation of guns came just a decade or so after percussion revolvers and rifles were the only thing out there and almost all had fixed sights. One thing I learned about shooting Pennsylvania rifle and cap & ball revolvers is to learn where they shoot and apply the ever popular "Kentucky Windage & elevation change" to my shooting or change the load until the gun shoots where you aim. I would suggest you first hold at the bottom of the bull rather than center and bet your results will improve. Also, if you are shooting lighter bullets, you will shoot higher.
If you have a 6" barrel, you will need a front sight about 1/16" to 3/32" higher than you presently have. Just a note that since I started collecting vintage S&W revolvers, I find that almost all that I own shoot high if I shoot to the center of the target, so believe it was common practice to focus on the bottom of the black rather than the center. That is what was called the "American way" when shooting standard targets with 6" to 8" bullseye at 60 feet.