Here is another issue with harness bars:
In a roll-over accident, if the roof caves in on you you have no method to move during the impact of the roof with your head. The seat side bolsters are restricting enough, add the full harness and you become one with the seat. By far the safest situation would be a roll bar. If you are going to do all the fab work just to help the harness bar mounting, why not fab a 4-point roll bar that you can (fairly) easily bolt in and out.
Oh...and before you nay-say the roll over risk, I would be glad to introduce you to a widow who lost her husband in a situation just like this. Had there been a roll bar or if he had a single late model type shoulder belt, he would have lived. A head and neck does not make a good crumple zone.
