I'm all about 2-post lifts, wouldn't allow a 4-post to take up space in my garage. If someone gave me a 4-post....I'd sell it immediately.
I just got done redoing my floor for a used 2-post I got at auction. It's a monster, I'm guessing at least 12K. My slab ended up being 3-4" variable thickness with light cracking, but had NO reinforcement--no mesh, no rebar. So I cut 40" x 40" squares out of my slab, dug down 18", and dug an extra 4" horizontally under the existing slab. So the footings come out to 48x48x18, but only look like 40x40 from the top. I also used rebar to tie into the old slab.
It was a LOT of work, but completely worth it. I did it the hard way (the cheap way, rather), and only used a skilsaw, diamond blade, 10 lb sledge, shovel, and HF cement mixer for the job. I'm glad I went to the extra effort required to make a 2-post lift work in my shop. I'd do it again in a heartbeat.
