Stamped block numbers below head

I'm looking for some information on the stamped numbers just below the head on an engine we are working on. The block is a 1971 360 casting and we think it is a Mopar Performance crate engine (early 300hp?). Anyway the numbers are HW560R3694. Across the number 5, at a diagona,l is stamped K-4 over the original number. Does this sound familiar?

When we took the Mopar aluminum dual plane intake off, it was clear that the heads and manifold had been gasket matched. Would Mopar performance have done that to a crate motor?