Hello Chris,
There is no way (at least no way I know of) to create a TField in the Field Editor for the DataSet component without indicating its size, so in order to solve this you have two solutions possible (and I had this problem myself):
1. Do not create the fields at design-time (this is the obvious solution and the easy one and I have used it providing I didn't needed to indicate some properties for the fields at design time)
2. The previous solution failed if we had to create non-data fields (Calculated or Lookups fields) because the TOracleDataSet only creates the fields at runtime if there are none allready defined, so, in this case you have to do that creation yourself. In case you don't know how the FieldDefs property has allways (after you calls its update method) the list of all the fields returned by the query and it has a method witch creates the corresponding TField component (Ex: FieldDefs[2].CreateField)
Hope that helped...