The article has been updated successfully.Yes, you can install and weld in subframe connectors on a car that is stripped down, on a rotisserie, doesn't have an engine or drivetrain installed, etc.
The most important thing to keep in mind is that however the car is tweaked before welding in your subframe connectors is how it will remain tweaked forever.
Check all of your door gaps and door opening and closing functions, etc. very closely. If your door doesn't close properly and you weld in your SFCs it will remain like that after they are installed.
Use jacks, measurements, levels, etc. to get your chassis as square as you can and all doors, body panel gaps, etc. as functional and visual as you want them to be and then weld in your subframe connectors to lock it all permanently in place.
