If you look at "Figure 4: Descent Vehicle Cartoon", you'll notice that the RTGs are far aft in the aeroshell. Plutonium is a very dense material. I suspect the vehicle's center-of-mass is very close to the RTG's center of volume. The hypersonic center-of-pressure will be aft of the 45 deg. sphere-cone aeroshell forebody. However as Mach number decreases, the center-of-pressure will tend to drift forward. If the center-of-pressure gets forward of the center-of-mass then the vehicle's aerodynamics will become statically unstable and the vehicle will tumble.

Using an RTG to power a cooler is a clever idea. However what typically kills a Venus lander is the heat accumulating within the insulated pressure vessel due to the electronics and battery, not the heat leaking in from outside. The refrigeration machinary inside the pressure vessel will generate a certain amount of heat. RTGs do not produce much power and refrigeration efficiency is limited by the Laws of Thermodynamics. The temperature of the radiator will be very high due to the ambient temperature on the Venusian surface. I suspect a pair of RTGs can not provide enough power to cool the payload at an acceptable equilibrium temperature.

The real issue here is technological risk: Is it more risky to come up with a clever refrigeration scheme cooling conventional electronics versus devising a system of high temperature electronics that runs at ambient Venus conditions? I suspect(?) there is less risk in devising a system of high temperature electronics (this is a tough call).

Gary