I'm not sure I understand what you need help with (and I'm not able to download your assembly).
If you need help with assembly constraints; try constraining to other things instead of the surfaces or faces. For example, constrain the center line of the shaft to the centerline of the scroll. Add some planes to both parts and constrain them Coincident to each other (or Offset). Use an Angle constraint to "clock" the scroll with the shaft.