If you go as modern as a Radeon dual-port card for this task I sort of suspect you're going to have issues driving that Portrait monitor. Any card that comes with VGA (instead of the old Apple 15 pin) monitor ports tends to have issues driving the old fixed-frequency monitors like the Portrait, the problem being that those monitors don't support the default "safe" video modes like 640x480x60hz and the monitor type detection mechanism for the old Apple monitors doesn't carry through VGA->Apple monitor adapters. You *may* be able to set it up manually or find an adapter "smart" enough to make it work but it'll likely be amusing.