273 dilemma

The only issue you will have is the pocket in the convertor flange for the nose of the convertor. In approximately 1968 they enlarged the diameter of the recess in the crank to accommodate a larger nose on the convertor. If you can find a '67 and earlier crank, it's a drop-in; if you find a '68 or later crank, it will require a spacer bushing to be pressed into the crank to let it match up to the '67 and earlier convertor.