Hi Lars,You probably won't like this answer but this is all so much easier at 10.1. At 10.1 sp1 we made a change so the NADCON transformation will no longer be added to the map by default, so it won't show up unless the transformation was actually set by the user. In addition, at 10.1 we added a new function call ListTransformations:http://resources.arcgis.com/en/help/main/10.1/#/ListTransformations/018v0000001p000000/It allows you to specify an input spatial ref, output spatial ref and optional extent object and it will return a list of all the valid transformations for the from and to spat ref. With this list you could compare what is in the map and select the match.