[Rich Biebel]

There were really very few small blocks that came with 2.020 and 1.600 valves, OEM...compared to the millions of engines built over the years

I also never saw any 461x heads with anything but 1.940 and 1.500 valves myself.

Many of the real early 1960’s castings were somewhat poor quality. Material seemed soft and the head bolt bosses were easily damaged.
Splits, cracks and other flaws were pretty common. Used to see spots that were welded by the factory occasionally to save a casting. Valve cover rail , deck, head bolt boss.