Since the engine was believed to have been rebuilt in the past, it is possible that the pushrod length was needing to be adjusted and they could have thrown in the ones that were originally in the engine and may be a little short. So when you torque the rocker arms nuts to 20Ft pounds, they stop on the bottle neck rocker arm stud as they should, and will not drop down any further so the rockers will not take up any play if there is any.
My next suggestion if you wanted to try this, is to make your rocker arms "adjustable." Simple enough to do this and if you have found a good mechanic, he will know what to do.
Your heads should have screw-in rocker arm studs. Replace them with Big Block 7/16" ARP Rocker Arm studs. Here is a set from Summit Racing: https://www.summitracing.com/parts/a...7101/overview/
My 1968 Service Manual says to tighten the screw-in rocker studs to 50 Ft pounds.
You will NOT
use the factory rocker arm nuts as they are too small in diameter (3/8" for the factory studs) and they will not tighten down because there is no shoulder (bottle neck) like the factory stud.
You will need a set of these Polylocks: https://www.summitracing.com/parts/c...6-16/overview/
Your mechanic should then adjust each lifter/rocker arm to "zero lash." Best to do with engine warm and running. May get a little messy, but this is the best way to adjust. Adjust 1 side at a time.
Put the polylock on all the rocker arms and tighten down so there is little to no play between the rocker arm and pushrod so the engine will run as normal. I would lightly snug down the allen screw, but not too tight, as the mechanic will have to adjust the polylocks once the engine is running.
With engine warm and running, back off of the polylock until rocker arm starts "clicking," then stop. Then begin to slowly tighten the polylock down until "clicking" stops. Wait about 20 seconds for the lifter to bleed down/normalize. If it begins to click again, tighten a little more until it stops. Repeat if necessary until the "clicking" completely stops.
Once the clicking stops, turn the polylock 1/4 turn more and lock it down with the allen screw - holding the polylock with a box wrench and tighten the allen screw. Don't over tighten the allen screw, but it has to be tight enough so the polylock won't back off. Your valves are now set for "zero lash."
Do this for each rocker arm. If the rocker arm/pushrod/lifter has any play in it, this should remove it AND your valve ticking should also go away.
You should not have any clearance issues between the valve cover and top of the polylock. If for some reason you do, you can buy thicker valve cover gaskets or double them up. Polylocks can be short or long in length depending on engine/rocker stud type and application. These should be the shorter ones and work on your engine.
And, if you should have to rebuild the engine somewhere down the line, these can still be used on the new build as well, so not a loss if you invest in the studs & polylocks.
This procedure should be no problem if your mechanic knows what he is doing.
Also, you posted in the wrong section.
We are not the 2004-2006 GTO guys.