I don't think they can even get an upper crossmember in there. Looks to me with the motor forward of the stock position, the shifter interferes with the crossmember regardless of how the shifter is bolted to the trans. This is in reference to the rear shifter position, not the forward one which would be wierd to use in an A-Body (IMO). So I think Holley had no option but to create a brace that fits under the trans instead of over the top.
In my case with the T56 Magnum, I have just an incredible amount of space on the sides of the transmission just because of making the floor flow into the ToddRon crossmember, which is sized appropriately.
Looks like that is one difference between the T56 and TKX. Based on the Holley instructions and DC Darts pictures, the TKX can leave all the OEM bolts for the crossmember while the T56 and the ToddRon kit removes the inner bolts and adds new ones. This leads me to believe that the TKX could have a much slimmer tunnel in the end. If a crossmember is built that goes over the trans, it would be taller for sure, but just maybe not as wide.
If some way could be done to do something similar to the Holley bolt in brace but with the motor in the stock position, the tunnel work looks to be pretty clean. But I could be wrong, just a guess.
