I don't know the spacing, but you should specify if you mean Merlin 61, Merlin 63, Merlin 66 or Merlin 70. All of those engines were used in Spitfire Mk IXs. The Merlin 66 was the most common, but a lot of people seem to think of the "real" Spitfire Mk IX as being the Spitfire F.Mk IX with the Merlin 61 like we have in AH.