Auto Parts: roller rockers on a 1974 corvette, hydraulic lifters, allen screw

Question
I just bought aluminum edelbrock heads with a roller rocker set up.  Can you tell me when i am adjusting the valves which screw gets turned first the allen screw or the nut. I have adjusted these several times with motor at TDC of that cylinder. I start the motor got it timed and adjusted. However after leaving the engine run for about 5 min the nuts on the rockers back off and become loose causing it to back fire throught the carburator. So can you tell me which nut or allen has to be tightened first.
thanks
Nick

Answer
    The nut adjusts the rocker, the allen screw locks it in place.  So you do the adjustment, then you tighten the screw to keep the nut from backing off.  If you are using hydraulic lifters, you must adjust a half to three-quarters of a turn past where the rocker contacts the valve, then lock it down with the screw.  You have to hold the nut with a wrench while you tighten the allen screw.  That keeps the adjustment from changing while you lock it down.