290, 343, 390 have a different crank flange (flat with no centering ridge) same as '71 401, 304 and rare 360. '72 up have the same looking crank flange as the 6 cyls with the same pattern. Early 6 cyls ('71 and older) are a small bell, including the first production 258s.
You need an adapter to hook the early motors to later trans (I found one for $200 to put my 290 in my Honcho, but will go with a brand new '71 401 flywheel rebalanced instead and run AX-15)