I looked for a set of connectors that would not drop so darn low on my vert. The biggest problem is the the lower seat pan box. I decided to get creative and use the existing structure and piece in my sub frame parts. Combo of 2" sq stock and heavy duty angle iron. I am still working on the connection points; though I should have it all dialed in this week. I can post picks or drawings of how I did it. Lots of welding, but I think I have come up with a way to create much better torsional rigidity, while maintaining, for the most part, ground clearance.
I have seen a few guys cut through the floor boards to accomplish an in the car subframe, but I think it looks like crap. I have an engineer, my father, helping me reason it all out.
I am also redoing the tunnel plate to add greater surface area, allowing me to "tie" in the two sides with much more stability. And, I won't give up access to the drive shaft, trans or exhaust.