[Mr70]

There never was a four row 1969 big block chevelle radiator.
It did debut in the mid '70 Chevelle big block though,coded either PA or PD.
As well as having to notch the top plate & the lower driver side frame cradle to make room for that 4th row during '70 production,they also had to hand shave about an inch off the 1969 Chevelles #3938165 three row fan shroud on the drivers side,as the lip there wouldn't let it fit a four row tank.
Many #165 shrouds were sacrificed,until the new #3976653 four row fan shroud became available during '70 and was essentially the same as the three row #165 fan shroud except for having that drivers lip omitted from it,among other things.
Then the current #6261914 four row shroud soon superseded both of them later on.