I did some mods to my 20 year old roll cage yesterday (Happy Canada Day!!!) and thought I would share them. I basically cut off everything back of the main hoop and replaced it.
We removed the curved rear stays that went to the plate you can see on the floor, put some 3/16" plate on and around the strut towers, new rear stays, cross brace, and increased the size of the strut tower bar to match the rest of the cage. I am not a fan of the angle the belts need to go to get to the strut tower, I may think of adding a harness bar later (had to cut out the old one that was on the old rear stays).
One thing that I am actually struggling with is fastening the window net. The way it was fastened before was a little hokey. It was attached at the top, and at the bottom, old seatbelt was sewn to the net, and clipped to the other half of the seatbelt slung around the cage. There really was nothing wrong with that per se, but I didn't like having to flip the net and this seatbelt clip onto the roof to get out. The roll cage is really close to the bodywork there and every time I come up with a plan, it puts the top of the net right in my eye line and too low for comfort. A different form of clip or buckle might even do wonders. I have old harnesses around, see if those might have something that will work. If anyone is still reading this, it would be nice to see detailed pics of how yours clips in and out.
Another pic because I thought the lighting was cool.