I had that size in my GTS, I went to 6 cyl bars and 60 ft went from 1.74 to 1.62, no other changes.
I think your car would be best with the 318 bars presuming it's not as light as an A body.
JMO Mick

69 Dart GTS 440 mopar .590 cam, Edelbrock heads, 3200#
best et 6.45, 106.78, 10.14, 132.88 mph, 1.47 60ft
best 60ft 1.36