It might have started with the OEM's refusal to share print specs, and the situation that most of the old prints are difficult to read to say the least.
Folks had to figure that out on their own, so everyone does it differently.
That is exactly the problem. Mopar Performance (or more correctly DC since it was a long time ago) could've solved this mess 40 years ago by releasing key dimensions. After they shut down big block production they had no reason to keep the dimensions secret. Had they just published key dimensions the aftermarket would have been able to produce parts that fit correctly.
