As far as weight differences between the two, Large American Gamefowl vary greatly by strain, I'd guess just under 5 pounds on the low end for cocks on up.
AGBs are supposed to be 30 ounces, but tend to range a bit larger, so 2 pounds, +/-. AGBs are more standardized in terms of conformation, toe and shank color, etc., as they are an accepted APA and ABA breed.