Lifter tick?

[My GTP 97]

Hello i am new to the grand prix scene..i recently bought a 97 grand prix GTP "LOVE IT" approximately 128k on it the guy i bought it off said the engine was replaced with a engine with 100k on it.He sold the car to me for $1400 and i couldent pass it up so i bought it.And after buying it..it dosent seem like he kept up on the maintenance so far i have given it new spark plugs "ACdelco" and spark wires along with oil change "10w30" and a intake.I didnt notice this light tick? on the back half of the engine until now and after doing some research only thing i could come up with is the lifters ticking or the spark wires weren't on all the way,well i checked the wires and they seemed on all the way. I made a video showing the noise.. if anyone could tell me what it is and how bad it is or how to fix it would be great thanks.

Heres the video
YouTube - Lifter tick??

[TheOtherNick]

Sounds like noisy lifters to me.

[My GTP 97]

Someone suggested i put marvel mystery oil in with my oil,i did that and let it run for about 5 minutes than drove it around a few miles the problem still presumes.. could you suggest anything to fix it?