Can you see if there has been any work done to my heads?

PanGasket said

No, it wouldn't. You would be better off getting a better set of heads. Even if you are pushing enough air in and out to justify porting them, those heads wouldn't really be the pick of the litter for that IMO. But I may be wrong, my experience is limited, but I know 273 heads are not known for being the best for performance

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I respectfully disagree with this. In an absolute sense, I agree. However from a cost/benefit perspective, I do not. The original 273 heads have the smallest combustion chambers of the heads Chrysler made for the LA engine. I'm slow to recommend new heads primarily for this reason. What I do recommend is that if hardened valve seats are not in the head, install them. Secondly, determine if the head has been planed, and if so, how much. If the head has been planed, I recommend shimming the rocker shaft an equivalent amount to restore the rocker arm geometry, which reduces wear on the entire valve train.