We installed the ones on Dads 72 Duster using the stock suspension and the car setting up in the air with all of the weight on the suspension. I left the wheels and tires on the car and used eight wheels 4 14" and 4 15"...It might look like he!! but it was very stable and worked out well...
If you get it up high enough it isn't a bad job at all...The doors on his car close just like they did in 72 and never needed adjusted. I'd install them again this way if I have to...
As mentioned above it does help to have something a little heavy to set in on the floor pan and help close the gap to the frame connectors when welding to the floor pan...Mine fit very well once mocked up...
Maybe next time I can use the 4 post lift...