From what you state, the "heavier" bullet impacts too low?
Normally, if sighted in with a light bullet, the heavier will hit high.
But, if as you say, your rear sight is raised to maximum, file down your front sight. The old adage holds true, move your rear sight in the direction you want your bullet to strike, move the front sight in the opposite direction. To raise point of impact, lower your front sight. This is easily done with a good file.
First sight in with the ammunition you plan to use. Set your rear sight at about mid-point of elevation. Fire five shot groups and file the front sight, say about ten strokes, between groups. You should see your groups "walk" up into the black. When sighted in, touch up the blade with cold blue.
No matter how desirable a collector's item it is, its worthless if you can't hit with it.