Finding the center of mass can be fairly simple (center of gravity).

Step 1 is to tie your suspension to your desired ride height so it doesn't move when you pick up the truck.

Step 2 is to tie a string or chord to the front of the chassis and hang it still in the air. The center of gravity will always be directly below the string put a piece of tape on the side of the chassis and draw a vertical line like you are extending the string.

Step 3 is to hang the truck with a string tied to the top of the chassis and draw a line extending the string through the chassis.

Where these 2 lines intersect is your center of gravity.