Swapping '69 273 with '84 318 Into My 1969 Dart

There is usually a clearance issue, fan to radiator. The cast iron pump is 3/4" shorter than the aluminum one. The timing cover is the same except for the timing marks and harmonic balancer. Plus will your pulleys line up. You have sorta planted your garden. Someone else will chime in here, I would have stayed on the 273 side, and radiator. Now your in-between the two. Plus, new aluminum radiators, depending on the brand, have a history of everything not fitting very well.