Okay, that sounds like a fairly reasonable deal. I would suspect there's a decent chance of GUC clearing from PS to D1 on day of travel given it is the dead of winter, but there is some risk there.

Something is not adding up however, as that flight is not currently showing Z availability and it is not currently available for direct upgrade from PS to D1 with a GUC. Did agent actually tell you it was available for immediate upgrade from PS cabin?