I saw photos of home builts and sat down with a notepad and tape measure and came up with this.
I have a very low clearance garage with a door opener I had to fit and spin under. I had about an inch clearance to spare.
The pivot points were 1 1/2" pipe with one size smaller inside. Had some play, but precision is not necessary to roll a car upside down.
1966 GT Fastback, restoration almost there! Code T Red with White LeMans stripes.
2015 GT Fastback - Deep Impact Blue