Do you mean the manifold outlet to the head pipe, or the openings mating up with the head? The outlets for a 67 are different on one side from 68/69 - I think the 70 manifolds are the same as 68/69 - not 100% sure. The other side is the same. From memory I think it's the left one that is different - rotated 90 deg.
This sounds close at least and likely 100% correct. The exhaust port on the heads & the inlet ports on the stock manifolds are the same, but the outlet location/direction of the exhaust manifold is different on one side. I've run headers for years & years, but I do remember something like that. Stock h-pipes might not line up & there might be some other issues too.