I had the same tick. I replaced all the lifters, sealed everything in the exhaust, verified timing, replaced rockers, push rods, and new injectors was still there. I just got a new Omega moose because of a turbo upgrade and the tick went away immediately. My old pump still worked but I had blown the shaft seal (leaked oil out the weep hole) and the reason I replaced it. My only guess is that a worn pump maybe loses some timing between the varying cylinders as it fires and creates incorrect timing on that cylinder (or cylinders). I dunno.
All the stuff I did replace I was happy i did anyway because they needed it after 170k miles but it was frustrating that nothing worked.