Big Block ticking? Flat tappet cam. Normal?

You could do a quick Test to determine if it is a valve lash adjustment problem or a valve train geometry problem.

Take one bank and set all the valves to zero lash. Run it for 30 seconds and see if that bank goes quiet.

If it still is making noise then it's probably a geometry problem with your 1.6 rocker arms.

Reset the test bank, back to the proper Valve Lash after the test.