Subframe connector installation

Ok fellas,

I need your help. I recently purchased some stock height aluminum body bushings from Global West and some bolt in subframe connectors from Competition Engineering for my 71. I will be welding in the connectors but my question is how do I install them? With the car on the ground, on four jack stands or on a 4 post lift? I've heard of body flex and the doors not shutting properly if not installed correctly.

Any help would be greatly appreciated!