Tom,
There is video out there of 463 and 315 double heading over Lobatto. I think there was a comment that this is the first time for a double header across the bridge in XX years. If I remember correctly, 463 can technically double head across with a K36, but any two larger engines must separate. Any combination of smaller engines are free to cross together.... Not 100% about the K-27 / K-36 combo, but I believe this is the borderline limit. So, for respect of safety, even the 27 / 36 combo will be split across....
Casey