Van's provides a W&B form with examples of various loadings of fuel, people and baggage along with a fore and aft CG range. All good.
But the example does not state which engine/Prop/spacer/panel/interior were used. Without an example close to your personal RV9 concept or a spreadsheet with components and moment arms it is difficult to forecast your empty CG location. Weighing the completed project at the end is not very flexible.
Install an O-360 in a RV9A and most optional items should move aft, Install a O-235 and things should move forward. But how much?