IMO the additional "BUMPS" & "divots" were to cut costs in the manufacturing process

the majority of 1970 covers "A" are what's needed - 2 different valve cover stampings
the first change "B" included the power brake booster "divot" on both sides
the second change "C" included 2 large "BUMPS" on each side

now the stamping was the same for both sides: piercings for holes & welding of shields/tabs/brackets made them side (and/or engine/body) specific