haha, the days of insanity was worth it. Did you use any framework for the grid system, I've always wanted to try making a grid-based game in gd
Nope! It is a flat array with a simple formula for the index:
index = row * number_of_columns + col
And the array stores references to nodes of a custom class called "BuildObject" which inherits from Node2D. It's a neat way to store all of that information.
I will probably cover it on my YouTube channel eventually, I think it's a really interesting topic.