360 hydraulic lifter valve lash

Your techs should stick to things besides performance engines because they are far from correct.
First - most 360s (not all...but most) had a special spring retainer used on the exh valves that rotated the valve more during operation. They are heavy, and are not designed for performance use.
Second, there is no way factory springs will correctly control the valve motion with that cam. There's a big difference between "working" and working properly and your techs missed the boat. If you stick a peice of styrofoam in place of a block of wood on a floor jack, it will take up the same sapce and visually look the same. However if you jack up under anything it will fail as it's not designed for the job you gave it. Stock springs are no different.
You must replace the springs, and you should replace the rotators. That is so you don't break anything and so the cam provides the performance it's designed to. My impression is that if you do, you may not have a tick anymore. Although you mention it ticked in factory form in teh 'Doba so you might just have a very worn lifter bore. In which case there's not much you can do unless you want to get into buying pushrods and rockers and even then it may not go away totally.