Some tips for install. Right or wrong, here's what I did.
Cut holes in the floor first so you can drop the cage down to weld the tops of the tubes. Easier to cut from the top side vs laying under the car.
Level the car.
Tack the 6 point bars in place. Level your bars, center the hoop in the car, use lasers, plumbs, whatever you can. Make sure your tacks are reachable so you can cut them later. test fit doors, seats, interior panels, seatbelts, whatever you're using or putting back into the car. Once that's confirmed, weld everything you can get to on the bars. Don't weld anything to the frame. Check and recheck all your welds, didn't miss anything, etc. Don't forget any mounts you're adding. Harness mounts, fire extinguisher, chute pull, whatever.
Place reference marks on your frame and cage so you can put it back exactly where it is. Cut your tacks and drop it through the floor and finish your welds.
While the cage is down through the floor, paint everything you can. Avoid the areas where you will weld later, including where the "8 point" down riggers will mount. It's much easier at this stage to get paint in those tight spaces and on top of the cage. Also install headliner if you removed it previously. Its probably easier to install your rear quarter interior panels at this time too.
Recheck level of the car
Jack the cage up into place and again tack it to the frame. Check level, all reference points, and burn it in. Check for missing welds, and paint the rest.
Go cry because it took 2 days.