When to start descent entering a racetrack under NORDO? Scenario:
I am flying in IMC, and communications fail completely. IMC persists up until destination, where I will be conducting the following instrument approach:



I am flying direct to ZUNAD from the north, approaching it on a track of 200°. When within the prescribed MSA, I descend and maintain 4,300 ft. At the moment I reach ZUNAD, I will be performing a teardrop entry into the racetrack/procedure turn (heading of 211° after ZUNAD for one minute, then right turn direct to ZUNAD).

Question:
Can I start descending to 2,600 ft just after passing ZUNAD, entering the procedure turn on that heading of 211°, or should I wait until I cross ZUNAD again and become established on the racetrack pattern?
You can descend from 4300' to 2600' as soon as you pass ZUNAD, as long as you remain in the protected airspace of the hold at ZUNAD.  

It is the same situation if you were "Cleared for an approach" in a non-radar environment.