Graham,
OK I did not notice that it is lifting the car on its sills / lifting point so the comment about it rolling off the tracks is not an issue.
Any car lift usually works by lifting the car then lowering on to locking clocks /racks. To lower you have to lift off the locks, get then out the way and lower. This is not happening here.
Also if you bolt the crossmembers to the lifting arms there is 100% a bending moment issue that.
1 The small high level fixings will not survive if one jack fails.
2 The bottom jacking arrangement is not designed for that load.
