Balance would be my first concern. It would take some digging and comparison between the 2 cranks but there could be some dimension differences. A simple thing to do is look up the bearings. If they are the same or the same size you are 1 step closer. Let's put it this way, I have never heard of anyone putting a 273 crank in a Magnum. I wonder the reason? Don't take me wrong but if the expense of turning a crank is an issue you are in the wrong hobby. Engine building can be expensive and you want it right.
