I believe both frames come drilled and tapped for the Weigand frame mounted scope mount. You need to remove your rear sight to access the holes.
Which ever you get, you will save a bundle if you reload. Factory ammo for both is very expensive.
I have three of the .500s: a 6 1/2" PC Hunter, a 5" John Ross Special and a 4". The PC Hunter has a built in Weaver rail . I mounted a Weaver 2x handgun scope in Warne QD mounts. With this setup I can use the scope, or pop it off and use iron sights. The gun is very accurate, but I tend to use wimpy loads in it at the range. With iron sights, it weighs 70 oz. With the scope, it weighs 85 oz. The extra weight of the scope really helps dampen recoil with heavy loads.