Hi,
The OP already has a 3.3V 20A PS but he wants linear regulator because he needs better stability for his experiment. He is not developing a commercial power supply.
The LT1038 that he uses can regulate over 14A when the input is 5V.
In theory the chip that gives the higher voltage may give all the 20A, you cannot match 2 chips by any means. In real life and by the specs of the device the output drops at higher temperature, it means that the other chip will come in as soon as the first one gets hot. It is likely that the chips will give similar current regulated by their temperature.
When one chip goes into current limit the output drops and the other chip shares the current.
With the recommended caps by the datasheet there will be no oscillations of any kind.
All that I said is based on my experience using linear regulators. I don't read articles in this subject because I think that my understanding of this subject is ultimate. I know that what that I'm saying makes you laugh, that's ok. I'm about your age and not much time left to repeat learning things, I enjoy more learning new things and that is good enough for me.