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the manafold is (I think) a cb-4 dual plane . Powerband is idle to 5500 Bill 58
Dual plane yes, but that is a large dual plane and is a good design, but still very much a "performance" manifold.
I will stick with my recommendation to use a 3.55 or a 3.70. I ran with the 3.70 rear gear in my 66 L-79 (327/350HP) Vette all over the interstates and tollroads in the late 60's and early 70's, and never had an issue. With your smaller 283, the torque and efficiency band will be at a higher rpm (with that combo of engine size and components).