Hi Terry,
Dimension alignment has changed considerably in Rhino 6. Until rhinoscriptsyntax is revised you can align the text in the dimension line by replacing rs.DimStyleTextAlignment
with:
...
import Rhino
...
ds.DimTextLocation = Rhino.DocObjects.DimensionStyle.TextLocation.InDimLine
doc.DimStyles.Modify(ds, ds.Id, False)
...