if you are only having a knock at wide open throttle i doubt its a loose rocker arm, because it would tick at idle due to the lower oil pressure. In my experience there are several things that could cause knock at high rpms.
ignition timing being too advanced
carburetor running too lean at wot
carboned up (sticky) valve or valves
running a fuel with too low of an octane rating
I would start by checking your timing. It should be about 12 degrees advanced at idle. If that is ok, I would try running premium in your next tank of gas, and see if that fixes it, if that doesnt work, I would re-jet the secondaries of your carburetor( if this is a factory engine with the factory carburetor you can ignore that, since that is likely not the problem, nor is the octane rating too low. If it is a factory engine that ran on regular unleaded all the time then it is likely the ignition timing too advanced or sticky valves)