[Mr70]

BO coded radiators were the standard,used on all M/T 1969 & 1970 L-78 equipped chevelles.
It's the standard 5.2Qt.,3 row radiator for them,not the Heavy duty 4 row.
That std. radiator used a 4 row passenger side tank,but the drivers side IA tank was a 3 row,used on all M/T & Auto Trans Chevelles.
Both of these years/models also used the #165 fan shroud too.
When HD cooling~5.9Qt. was ordered on a BB 1969/70 L-78 Chevelle,the factory swapped out the Chevelles drivers IA tank for a wider 4 row tank turning it into either a PA~M/T or PD~A/T coded radiator.Also shaving down the extended fan shroud lip,both on the drivers side and bottom of the #165 shroud,to now accommodate the 4th row.