That tick is nasty, and I would not run the engine too much with it slapping like that... If there was no tick prior to changing the rockers, I wonder how it was introduced? Where'd you get the rockers? New, used? Did you ever do as suggested, check the pushrods? There is a bit of diagnostic you can do to help yourself before blowing $ on parts. I asked if you torqued them correctly, meaning torque the rockers, then rotate the engine and torque again, if you wanna be sure, rotate once more and torque all rockers one last time... Lol... The bolt could be the problem too as you reused the TTY. Can't see how all of a sudden the lifter would tick because you changed the rocker. But all else being equal, if everything is good above, (valve train), then the last piece that could cause that is the lifter.