Jester is correct that early hemis had fairly radical valve train geometry and they need to be set right or won't perform. Valve float could be a problem if your running a high lift cam and using stock springs, especially if they're original to the engine. However, if your running any cam that has a higher lift than stock you need to run adjustable pushrods, otherwise your valve lash will be WAY off. Another thing to think about, 10:1 compression is on the ragged edge when it comes to pump gas. Try a 104 octane booster and see if that helps the pinging.
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