The c/g will come out behind the main gear, so... . Find a table that you can set the plane on while hanging the main gear over the edge. Get a piece of 2" pvc pipe about 3 feet long or so. Make a mark on the bottom edge of the fuselage where you want the c/g to be. Set the fuselage on the pvc pipe, 90 degrees to the pipe, hanging the main gear over the table, and not letting the tail wheel touch the table. Don't forget to place a wedge in front and in back of the pipe so it won't roll!! See where the plane balances in relationship to the marks on the bottom of he fuselage and add or subtract weight from there to hit the mark. Sounds complicated but it's actually very easy.