If you can find an Ambrosio Excellight rim, that should have a compatible ERD. The last Open Pro I measured had an ERD of 603mm. But if you have straight gauge spokes, you may want to consider replacing them with butted spokes while you are already replacing the rim. In that case you have lots of rim options. The A23 rims previously mentioned are nice. For a 32 spoke PowerTap wheel, I would lace the spokes cross-2 and not cross-3 in order to get a better spoke line.