I agree with J above.
I used the cross member mount for my harness. These were set up by Superformace, and they would assume the liability for the cross member mounting. The cross member is as strong if not stronger than the roll bar. Being part of the rear frame it also attaches the uprights for the shock mounts. You can view this on Superformances website.
I was told the the shoulder harness mounting should be no higher or lower than 2"-3" from your shoulder height. To avoid injury in a front/rear or roll over. If the mounting is lower, bottom seat or floor you can get spinal compression. If the mounting is to high you would not be secure.
Removing the rear tires makes mounting must easier...
