I think all threaded holes are drilled and tapped later into the finished casting.
It appears the early corvette 235 cam and head setup was the model for the following 58-62 stock 235s.
All they need is a dual intake and exhaust headers to wake them up...
Interesting also that the master parts book lists the 261 cam for 53-55 corvettes as well as the 848 head up to 57 corvettes, despite 235s no longer being used after 55.
