As you know the 1300 is a pump and the 1400 is a auto . IMO if you drill in the port(s) in the right spot and angle it should work. I would have a gun smith or machinist do it . EDM the port(s) would be better . If you drill the port ,I would try 1 or 2 drill sizes small to start and see if the gun works . You can allways redrill with a larger bit ,harder to put the steel back .
Good luck