I’d say go with the 62 heads and try to keep the date code in line with the engine / intake etc. you already have. Your only other alternative would be to find a complete engine in the timeline you’re looking for but that as you know is a difficult & expensive process. I did exactly this for a manual WQ engine which I found with mid May 1969 build date. Unfortunately the block had a crack and was unusable. 2 years later I found another WQ block built end of May 1969 that was usable. This block had the ‘70 P/N and date stamp on it yet had the earlier motor mount bosses only drilled. Emailing with Rocky Rotella I found out that this wasn’t highly unusual as the had already started build of the ‘70 Components at that time and as ‘69 production ran late than planned they needed to use what they had. Ironically, neither of these blocks were ever VIN stamped.
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