I would do as suggested and weld them, much less flex factor, IMO.
First order of business is to make sure the car is LEVEL. Place jack stands safely under the LCA's or blocks under the tires or both. Place jack stands under the rear end. You will want the full weight on the suspension.
Level, level and level! After you have the car level make sure your doors open and close the way they are supposed to.
Clean the areas on the frame where the holes are and plug weld in that area and then around the outside edges.