This is how my 4 post is with the jack trays that i am talking about.
The trays are made from heavy angle iron and slides along the bed. Nothing sticks above the level of the tracks. I have 3" ground clearance on my car. After the car is on the lift I use a couple of HF 10 ton bottle jacks on the trays to do the jacking and use 2 big red jack stands on each tray to set the car on them when working on tire or suspension work.
The company is no longer in business but other have the same design.
Also my uprights are made from 1piece box tubing with safety notches cut in them. Some lifts use a "U" channel upright with safety stops welded in. I had to anchor my lift to the floor because when I tried to drive my car on the ramps it pushed the lift away.
I used 4 HF small furniture dolly under the front and back and lowered the lift down on them and the uprights will move by pushing it in place. Sorry for the mess but I ran out of room.
ritrebor