[69gmcc10]

The holes in the crossmember that the trailing arm mounts mount to are already there and you can just bolt them up or drill 2 holes in the crossmsmber to flip the mount for a better traction.

Where the lack of holes to bolt the crossmember to was referring to the upper shock crossmember that is needed to mount the upper shocks, locate the upper spring retaining bolt, and strengthen that area of the rail. It is easy to locate the holes if you flip the crossmember upside down and backwards then center it on the oval reference hole on the side of the frame rail that locates the crossmsember and use the crossmember an a template for the hole locations on the top and bottom of the frame rails.