I believe there are at least 3 different RH (passenger side) valve covers that were used on big blocks for the 1970 & 1971 model years

A * narrow oil fill & no "divot"
B * narrow oil fill & "divot"
C * wide oil fill & "divot"

trying to determine when the changes took place

who has a late '70 or early '71 model year big block car (B, C, E-body & 383 or 440) with it's original valve covers: that can share their car's valve cover style, scheduled production date, engine assembly date and assembly plant info?