Determine Usable Fuel Qty....
I have a neighbor that talks of deliberately shutting down the engine of a single engine airplane in flight. I could look again, maybe at an update, but don't believe that procedure is called for in the FAA AC on experimental airplane flight testing. Enough said.
One probably safer way to determine usable fuel, in flight if you must, is by using the boost pump. When it cavitates, it makes a lot of racket, but there is still time to switch to the other tank, while keeping the engine lit. Then land, fill the empty tank, and you've just determined usable fuel plus whatever might be in lines, carb bowl. Fuel temp matters, but 59F+- should be close enough.
Alternatively, you could more safely do this on the ground by getting the airplane in a given pitch attitude, remove the fuel line where it attaches to the eng driven fuel pump, and run the tank out/dry using the boost pump into a fuel container. Refill tank and get the usable fuel qty, verify gauges etc...
Back to in flight engine restarts. Should get turns you need to fire mags/plugs from windmilling, but not a good time to have a weak battery, starting system, or degraded fuel system, eg boost pump, etc..
Link McGarity
RV6/N42GF/FD38
Wellington, FL