Anything is possible and lots of places for wear and all sorts of noises in the process. Lifters can fail too, or get cloggedI'd put the rad back in, run it on water and get a long screwdriver, get it running before you go any further with this... Further that and check all the rocker clearances to rule out a tapping valve. This could go sideways expensively if your not sure about finding the real issue and just throwing new parts to find a deeper more concerning problem that may end the project abruptly!
