Run With The Fox. First I would like to state that I am no where near the authority on Fox guns, many are much more knowledgeable than me. I have only handled one Becker gun and it was a 12ga. I did not measure the bores or chambers.
Bill is correct measuring the frame is the only positive way to determine the frame size. I also agree that a H frame gun with standard bores documented as 8 plus lbs would be of interest to most Fox collectors.