A messed up pushrod or other valvetrain parts will result in a dead miss on one cylinder and some 'clatter' A bad rod or main bearing will cause a noticable "knock knock" sound when running, but less likely to have a dead miss. A compression test on all 8 cylinders will tell you if you have a bad pushrod or other bad valvetrain parts. One cylinder will have very poor compression PSI, the other 7 will be much higher.
good luck
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