On the moroso chart, 128 is a 10.39....... So it's not way off.

128/4.10's/28" = 6300rpm, so the converter slip is 8%, which is pretty normal for that type of combo with an 8" converter.

If you do end up swapping the cam, I agree that a dyno session would be a good idea.
That way you can tune it up and will know what it "should" run.