We have not used spelt flour in the recipe testing, but think it should work well.
Several articles online mention that it has similar baking properties to all purpose flour.
To begin with we would recommend you follow the wholemeal recipe and substitute the wholemeal flour with the spelt flour (so 2 cups high grade white flour + 1 cup spelt flour).
If this works well you can slowly increase the proportion of spelt flour in future batches.
See here for our How to Guide.