Bill, I'm not sure I understand your question:
What is a "production block"? 390, 428
Are you asking the weight? If so this thread probably will tell you more than you want to know.
Weight of 428 bare block??
Except for weight I would suspect the main difference between those two stock formula KC engines is the displacement. From being in his shop a few times I've seen that he does build certain formula or "crate" engines because I saw a whole row of identical 482 FEs wrapped up to go to Kirkham as needed. But, he is a custom shop and KC will make any number of changes in a engine build to suit what you need.