IMO
NOT rebuilding the upper hoop is a mistake.
Sure, you can do it. and Sure the car will be fine sitting in your driveway.
But what happens when you swap out the slanty T-bars, for 340 bars or 1.03s? and you drive it? Most of the forces that cause the wheel to go up and down, are transferred into the T-bars and from there into the X-memberS. What happens when the bolts holding the X-member slip? and they will.
The factory X-member is a tie-bar to the hoop; together they transfer the T-Bar forces into the Unibody. Neither of them alone is sufficient. If/when your X-member clamping bolts slip, the whole thing will work itself loose, Be flopped around by the T-bars which will tear out the floor, and then bang out the holes. While that is going on, the Z-bar is drooping, and causing departure woes. In what order this will happen, or how long it will take, I cannot say.
As for the supplied X-member, I cannot say either, I haven't seen it.
As for me. I want a hoop there. And I want to raise the tail to factory height to maintain the factory driveshaft angles, for the factory ride height.
If you change the ride-height or change the power input, you have to rework the rear pinion angle. The 6-cylinder rear springs will have to be replaced if you keep the factory-type suspension.
You can ignore this and endure the consequences which are.
Noise, Vibration, Harshness, and broken parts. Not to mention lousy handling.