This is just my 2 cents, but I would ask what you intend to do with the tractor. If you were just going to use it and are not worried about the restoration, then repowering it with the Cummins would be OK. However if you are more concerned about an accurate restoration, then stay with the 310. Were you going to overhaul the 310 engine? A quality overhaul should be good for a long while.
Another thing to consider is if the tractor is going to handle the additional horsepower. 50 additional Hp. may strain other parts of the tractor.
   I recently overhauled a Minnieapolis-Moline 504 engine.... I sure ended up with a lot of time and cash in that project.... much more than I had initially intended, but a good engine now.
        Good luck with it!
              Cal