It is very easy to trace lifter noise. Very easy (but can be messy). Try to first determine which side, now with the engine running remove that valve cover and with a hammer handle put pressure on the push rod end of the rocker arm. When you hit the noisy one the noise will diminish or stop. A lot of the times it don't come back after purging the lifter in this way. On a relatively fresh engine you shouldn't even have to take any more than the rockers and push rods off to change out a lifter. Are you even sure that it is a lifter tick and not a manifold/header leak??? there is also a lot of times a certain amount of rocker noise with OEM stamped rockers do to their loose fit on the shaft. Won't hurt a thing. Doesn't sound any worse than solid lifters.