I started down that path and now about the only thing left that’s original is the frame.

For me the biggest thing was moving the power supply under the back of the printer and putting 90 degree die cast braces to support the tower. The tower is the critical point of rigidity in this kind of design, and the stock ender 3 oscillates like a tuning fork. Especially if you leave the roll of filament on the top and the power supply attaches to the upright.