I talking power wise, 318,340,360 manifolds have little difference in hp, can't see 273's be that much difference power wise than a 318, especially on lower powered engine.
I should have quoted @Syleng1 The 64-68 A and B body RH manifolds are the same number. The 64-66 A body LH manifolds are the same number and the 67-69 LH manifolds are the same. 273 stopped in 69 so they were 318 manifolds from then on.
