Some assembly required.. From the guys I talked to who run stockers it is more beneficial to replace the 64-66 915 head than the later 906 head since the 906 is vastly improved over the early head (they have a secret way to fix the aluminum head). Also there’s so many later heads-cars out there that NHRA has a better handle on their HP than the early low performance engines. The racers are always looking for the killer combo but eventually NHRA catches up.
What there really looking for is a iron 452 BRAND NEW casting identical to the original to just do a valve job and run them.