||We do support Stereo 1970 (based upon Dealul Piscului 1970 datum). To define data with this coordinate system, use the Define Projection tool in ArcToolbox. Use the Select button to browse to projected coordinate systems, national grids and select "Stereo 70".
To convert data in Stereo 70 to WGS84, you can project it on the fly in ArcMap, or use the Project Tool in ArcToolbox. In either place, you will need to set a geographic/datum transformation. We have one from Dealul Piscului 1970 to WGS 1984.