Hard to argue with a man who has done it. I concur that if one head is leaking the other one cannot be too far behind. Additionally we have 30 year old valve guides to consider so both heads should probably be done. Plus you are already pretty far in to the engine and have the timing belt off at that point. I was thinking that with one head off there would be more room to shift the engine driver side and the other side would be relatively easy. Of course that means getting one side off first.
I think about this stuff wayy to much and really don't want to pull the motor.
So, The in frame process, even IF possible is impractical, and a better course of action in the long run is to pull the motor. Sigh.....
Sorry to hear you may be in the same boat. Seems to be going around. These 30 year old parts tend to need replacing. Go figure.