Thought I'd talk a little about the reasons for the cage design. We decided to do a roof halo above the roof mostly for head clearance. An inside cage puts the tube very close the your heads when you're wearing a helmet. Rules spec a minumum of 3" of head clearance to any tube, and there's no way to do that on an XJ with a totally internal cage. While it would pass tech because there's just no option, we though the external cage would be safer for our own heads. Plus, because it's an Ultra4 car, and so we race in rocks, if we do lay it over we have some roof protection. We can also get away with the look of it because it's a rock racer.
We would have liked the outside of the halo to be further outward, better to protect the roof when leaning the top against rocks, but rules specify that all cage tubes must intersect, so the down bars had to meet the halo tubes. I made the down tubes as far outward as was possible without dramatically removing sheetmetal and ruining any strength in the stock structure, and made the halo the width to meet those tubes.
It would have been nice to make some sexy bends in the down bars, making it a little more cool looking and getting the bars closer to the stock B,C, and D pillars, but to whatever degree the bars angled in at the top would make the roof halo narrower. So, I made the down bars straight and as outward at the top as possible. Straight tubes are stronger than bent tubes anyway. Also, the rules specify that foot plates cannot be welded to sheet metal, they must be bolted using backing plates, so the A, B, and C pillar foot plates are bolted. A D pillar hoop is optional, plus that foot plate is over the frame, so that foot plate got welded in, which also strengthens above the rear shackle box.