Easy enough , and not super expensive to figure out , get another pair of heads , or at least replace one... BUT I'm pee in the punch, thin cylinders on that bank COULd be putting more heat in the coolant on that side and causing it to run hotter , or the coolant is somehow being restricted.

One way to figure out if it is the head that is causing it , swapp the heads side to side and see if the heat moves. I'll supply the head gaskets if your're up for the challenge. If you lived closer to NH I'd do the work.

This is getting interesting.