I don't think it would work in this situation since Holley moves the motor forward with their swap parts, but it kind of says to me that they feel the crossmember needs to be reinforced when the middle is removed.
That first link is only the lower crossmember section. But... the hoop is *fantastic*! That is perfection, you cannot get any better than that. If that hoop fits the TKX (or could be made to fit it), that would be the end-all be-all solution. The price is awesome too!
That's good thinking, but no, because the trans is bolted to the lowest section of the crossmember. So even though its position suggests it would complete the triangle, the forces would only travel through the mounting points, which are at the bottom. In other words, the t bars are also pulling the transmission toward the ground when you hit a bump (but that would not happen if you connected the crossmember at the top).