I have to agree with BW. It sounds exactly like you ran out of gas. It's a little strange how it happened but has the out of gas symptoms.
The Shelby race Cobras never used a fuel pressure regulator at all. they ran the cars at 5-7 psi depending on what rpm the engine was at.
At 3500 rpm you would likely see 7 psi and at the red line, likely 5.
It is absolutely normal for these freakin' things to backfire through the exhaust when you suddenly close the throttle like you would decelerating going into a turn.
I never could figure out why but ALL of the
Weber equipped cars do AND if you are behind one you will see a small flame out through the exhausts.
Have someone start the car in the dark for you while you watch the velocity stacks. You will very clearly see flames in the carbs. It's really freaky.
My neighbors kids, when they were small always wanted to watch me start the car in the dark. They would start screaming in joy at seeing the exhaust flames.
The real danger of running dry on fuel is at wide open throttle. The engine will suddenly backfire violently and it's to the point that it will bend all of the throttle shafts.
My opinion is that when you are racing the car, your fuel supply should be unrestricted but no more then 7 psi.
You can do that by using a 7 psi electric fuel pump that feeds a Holley HP mechanical pump. Neither pump will give you more then 7psi either individually or together in tandem
On the street you are PROBABLY safer with a fuel pressure reducer? Probably. I have no way of proving that scientifically though.
If you haven't already installed glass ball inlet valves, you need to. It's not a bad idea to use the solid nitrofil floats either but you can only get them from one of the VW racing guys here in the US.
That way there is no way you can collapse the brass floats or overwhelm the original inlet valves. The original Weber ones were always questionable. I don't know what they were made out of but at least Holley uses Viton in their's.
The glass balls don't care about ethanol in the gas. The "rubber" ones do.
I love the picture of the car. Great shot.