Hi Scott;
You should definitely see a voltage drop across R77 when in transmit. When transmitting, one side of R77 is connected to +12 Volts, and the other side is connected to D6, a 5.6 Volt Zener diode. Please check again. It's possible that the Zener diode has opened up, or that some other part in the PA bias circuit got fried when the FET failed.
Adjusting the PA Bias pot will have no effect on current until you get close to the point where the FETs begin to turn on - then current will begin increasing rapidly. Your description of the PA Bias pot behavior sounds correct.
Transistors Q12 - Q16 are still in the transmit chain on a fully modified DE. They are known to get toasty hot when in transmit. I can see them accounting for the 300 mA current increase. (I haven't bypassed Q16 and Q17 driver FETs in my DE, so I can't compare results with your DE.) You can measure the voltage drop across R19, R20, R45, and R48, and determine the current being drawn by each transistor using ohm's law. Don't forget that these four resistors got replaced with new resistor with a lower value (The V2 has 4.7 Ohm resistors in these four locations.) Gordon KX4Z and others have provided voltage drop measurements at these four resistors here on the BITX20 forum, so you should be able to compare your readings to those previously stated here.
73; Steve, N3SB
