You, not your machinest, should check the crank for straightness in a set of V blocks. My second thought is debris in the oil passages before engine start up, is the camshaft okay on all lobes Measure the actual lobe lift on all lobes, easier to do in a lathe The very first motor I put together after a minor overhaul did the same thing as yours looks, my camshaft went flat do to me being yuong and dumb, used lifters on a used cam BTW, I've done worst since then like breaking a rod in the lights on my original numbers matching block in my 1963 M.W. 415 HP stocker