Gaining access to Jetson Nano PCIe port via interposer

The very limited space available from the M.2 connector makes access to the PCIe functionality of the Jetson Nano difficult. However, 4 lanes are exposed by the test points on the bottom of the carrier board. It should be possible to build/fabricate an interposer that can robustly pick up the lanes and convey them to a more useful media such as the end of a USB3.1 C connector. Normally, there would be a silkscreen that would identify TP81-TP96, but not in the case of the Nano, at least, that I have been able to identify.
Is this information available?

For now I’ll just assume the logical and that for each of the transmitting pins it’s receiver is directly opposite.

Normal hardware development would utilize a loop back, first directly and the board, then a short loop back cable, and so on all the way to fame and fortune:).

Don’t suppose anyone has any test code handy they would care to share?