so, tapping type noise apparently coming from the centerish area of the top of the engine. sounds like its coming from under the lower intake, but it could very well be resonating from under the valve covers. its a tapping noise, increasing and decreasing in speed with the engine rpm. sounds to me like it is coming from more than one spot, i would guess 3 spots. like, if it was a lifter problem(i have no idea if its a lifter problem), it isnt just one lifter, because of the pattern of the sound.
regardless, im taking the top end apart down to the block anyway to replace seals, is there anything i can do before i take it apart to perhaps narrow down what im looking for to find the source of the tapping?

 

can it can be a few things, the most common is incorrect valve lash.
what are your heads, cam, rockers, and the pushrod length?