It's at 73 challenger.
The pistons do come above block deck the standard height for a 69 340. I don't recall the exact numbers.
I built the motor and lined the timing marks up for the timing chain. They were perfectly aligned. I'm not knowledgeable as far as degreeing a cam goes. I have built 4 motors and installed at least another 4 or 5 timing chains. I have always aligned the marks
Not sure how to check if the secondaries are opening. I installed a Street Avenger because I don't have a lot of expertise tuning carbs. I have rebuilt a few but I am by no means a tuner.