10 Day Magnum Swap - '65 Dart 270

ValiantOne, I am by no means an expert on old school mopar HiPo parts but the 340 HO manifolds I have seen have a much taller exhaust port and it appears that the height was taken from the floor of the exhaust port. I have lots of gaskets around here from various LA builds, Fel Pro, Mopar, header supplied etc..I only know of two exhaust gaskets, standard and tall port. Just my personal exp and by no means accurate or complete, I am a magnum guy and I know them very well but some of the early stuff eludes me. I have compared 273 and 318 since I have a few of each here and they are as close as a "gasket match" ie not more than about 1/8" all the way around in size difference while the HP 340 are more like 3/8" but mostly on bottom of port, taken from looking at gasket not actual manifold