First of all, welcome to CHR captnmike! Hope your stay here is long and that you find lots of good advice as well as share your own stories. If your avatar is the car in question the ‘66/67 Chevelle is one of my all-time favorites and your’s looks to be a sweet ride.

I absolutely concur with others that level should be checked in neutral and warm but also agree with B&M, re; sloppy shifts due to foam. As set up, the fluid drains to the transmission and the cooler when cooling off and leaves air in both lines. Until the air is completely purged and there is an uninterrupted flow of fluid from the transmission to cooler and back to the transmission you will have foam and poor transmission performance.

Heat kills automatic transmissions. The fluid is a much better means of dissipating this heat than air. Air and foam, even for a few minutes, can lead to problems in your transmission and shorten the usuful life of the clutches. If this were mine, I’d be tempted to re-plumb the cooler. In front of the radiator is the right spot for the cooler, but I believe that if you were to construct new lines from braided stainless lines using AN fittings and run them along the frame rail it would take care of your issue. Braided stainless gives you lots of flexibility and looks great too. That way, there would be no “up-and-over” for the fluid and you could do +/- 11-1/2 quarts and know that the fluid level would be correct.

Once again, welcome and let us know what you decide.
Glenn