Engine Vibration 3k RPM

A trick I use that may help, I hook up an inductive timing light and run it on all wires, I point the light at a valve cover or inner fender well something similar the light will blink intermittent on any cylinder that is missing..it will look like an erratic flashing sequence. But back to my story I had also though I had a balance issue on my 340, I swapped in a 318 vibration still there..it drove me crazy...I did alot of wrenching and back wrenching on that car that was 2003 almost 20 years ago...

340 is back in car since 2008,and 318 sitting there collecting dust...:)