Depending on the year of your 318,
The deference could be the pilot hole in the center of the crank for the converter. I an not sure of the year but the early small blocks have a much small pilot hole, than the later ones. I think all 273's are the smaller hole. Really narrows down converter selection. But I to have been thinking about using a foraged 273 crank on my next engine. I would think any machine shop could open the pilot hole up to the later size. At least that is my hope!
