Head Job resulting in a knocking/ticking noise

Hey guys, I just finished replacing the heads on my brother's 91 notch. He had blown the head gasket so I tore the top end down and put my old heads ('93 stock heads) on instead of sending his off. My heads came off my stang a long time ago for cobra heads. There was nothing wrong with mine when they came off. Got the whole thing back together and we have a knocking/ticking sound when we start the engine (not an exhaust leak). It sounds kinda like what the plastic end of a screwdriver hitting the stock valve covers would sound like. It is proportionate to the rpm. I pulled the valve cover and checked the rocker arms studs; they were all tight (torqued them to 25 ft/lbs when I put them in).

Anyone have any ideas as to what my problem may be? I did not touch the bottom end, only removed the heads and all associated with that. I did have to use the rockers from his old heads on my heads. Any advice would be appreciated. Thanks!

-Ken

I'm pretty sure I put the rockers n push rods in the same order they came out. I did notice when I was turning the crank while installing the rockers that one of the lifters (the component in the block below the pushrod)(just not sure if that's what it's called) didn't go all the way down without some help.

Is adjusting the valves equivalnt to bringing each cylinder tdc and torquing the rockers again? Sorry, kinda new at this.

Wanted to post an update to the thread I started. I got the ticking/knocking noise fixed. It was the rocker arms. I loosened them all and snuged em down and them turned the crank a few times. Then I checked and some had come loose so I retightened them. put it all back together and no noise. Thanks for the replies. Stang feels strong now that the head gasket is fixed.