I'm here to report that - even though the cards flash successfully with a variety of ROMs found >HERE< - they do not function correctly afterwards. Some become too hot, some report vastly inaccurate hashrate readouts, others are stuck on 30W power limit, and others have the fan settings stuck on some value that cannot be adjusted.

Ultimately, they were all limited by power (down to 30W), and had issues with hashrate reporting.

My P104 GPUs are by INNO3D.