To break it down into simple terms:
i have a mustang, that originally was a v6. I swapped the motor to a 97 4.6 2v that i did a complete overhaul on, as well as comp 270ah cams and trick flow lash adjusters. Swapped the trans to a T45, and rear axle to an 8.8, and swapped every hsrness in the car. Recently, I decided to do a PI swap. Bought a set of heads, had them cleaned, resurfaced, valve job, and the thew them on accompanied by arp head studs, new chains, new chain guides, and new tensioners. I got the car running, and when it first fired up, it ran great. Its also worth nothing i threw 30lb injectors in, even tho the car isn’t tuned for them. Even with the 30lb er’s, the car ran smooth. No belt accessories were hooked up, we simply hooked fuel and ignition up and fired it. NOW, we put the car all the way together and it makes a tick/tapping sound, and will stall out if you try to drive it. Originally I thought it may just be a lash adjuster or cam follower, but i have no idea now. Also, car back fires when its cold, have to hold it at ~2k for a sec for it to idle. ANY INFO HELPS. Here is a video of it running:

Thank you for reply, i’m going to look at the plugs and pull them out and inspect them. Maybe ill find something.. im also going to pull the pass. Valve cover and turn it over and watch for oil. I am suspecting and oiling issue maybe? The first time i pulled cover it looked dry