slant six starting problems

Are all voltage measurements relative to BATT- at the top post of the battery itself (not the terminal)? Is BATT+ above measured at the post or the terminal side? I once measured an 8 V drop between the BATT+ post and the cable. My wife had called, stuck in a parking lot, w/ a "no crank" situation. After measuring, I removed and cleaned the post & terminal, then got 12 V at the terminal and it cranked and fired instantly.

Some of the voltages above seem a bit low. What really matters for the spark system, is all voltages measured relative to the case of the ECU, since that is the return path. If you read and followed prior posts, you already ran a dedicated ground to the case, so it should maintain the same voltage as BATT-, but prove that with a multimeter.