There isn't a need to put headers on, or even change to RA manifolds for that matter, unless you're trying to eek out those last couple of hundredths at the track. I'm running log manifolds with the 2 1/2" Pypes X system. With a 462, stock intake, stock cam, stock heads and Summit 2802 cam and 3.08 gears my 4100 lb. Lemans will run in the high 12's. So the logs should be fine on your 389.
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1966 GTO
1969 Lemans Convertible- F.A.S.T. legal family cruiser. 12.59 on G70-14 Polyglas tires. 1.78 60'
1969 Bonneville Safari- cross country family cruiser. .
1979 Trans Am 400, 4-speed, 4 wheel disc.
View from the drivers seat racing down Atco Raceway-
http://www.youtube.com/watch?v=GhYDMdOEC7A
Ride along in the other lane-
http://www.youtube.com/watch?v=mIzgpLtF_uw