340 exhaust manifolds

You better measure the height of your exhaust port on early 273 heads. The 340 exhaust manifold port is taller.
I made this mistake on my 67 273 and although they did bolt on, they did not fit. The flat sealing surface of the heads is not big enough on the bottom and it left a 1\4 inch gap. I am now using magnum heads on a 340 and it just barely seals.