revisit the fuel gauge and sending unit issue

Whether you are spot on correct about how much fuel is actually onboard or not, the linear sender is the problem. The linear sender has a 80-10 ohms range and will show you those end points at the workbench. It will also show 35 ohms at 1/2 range. The OEM thermal gauge needs approx' 23 ohms signal to point its half range. That 35 ohms is within needle width of 1/4 hash mark on the OEM gauge screen. You might be able to verify that with your homemade tester if you wish.
Bottom line, every ohms value between end points of a linear sender is wrong. A meter match module will correct this. In any case your 53 ohms would be well below the fuel level you submit to having. I'll go ahead and add... My 67 isn't driven often. I fire it up at least once per month and let it run 30 minutes. I might move it to wash it. I might blast off for a 20 mile or 50 mile run. More often just sits and idles. So the odometer reading is no indication of how much fuel was burned.