This is where the difference lies... and I support @331MP in his thinking. Unfortunately, times have migrated into forcing racers to CNC prepared parts.
@LO23M8B also makes a COMPLETELY valid point concerning the Stock, Super Stock guys.
In fact, I have a anecdotal story that is hand in glove...
20 years ago, there was a local guy here (friend A) that had aspirations in running a 440 6Bbl in SS. Beings he was friends with another local guy, who campaigns a shivi in SS (never qualifies in the top 40 at national events) and runs a business porting heads, it was a natural to use him.
My friend gets his heads back (906s of coarse), and asks, 'how do they flow?'... 'don't worry about it' he reponds, '.....they flow good'. They did look 'ok', but I didn't like the VJ.
Naturally, not being satisfied with that answer, friend A takes said heads to friend B and throws them on the bench and found numbers that would probably never got him TO the national index, much-less BELOW the index.
Lesson learned, and the job had to be re-done.