Saiga 12 Barrel Contour, Need Info

Does anyone have the measurements on the Saige 12 gauge barrel contour?

I'm interested in the barrel diameter where the gas block and the rear sight mount are mounted.

I want to build a Saiga based 45-70 rifle for pig hunting. Was going to use the 410 as the base for the conversion but I want use a heavier barrel. I was checking to see if the 12 gauge would be a better starting place because of the larger diameter of the gas block and the rear sight mounts would allow me to use a heavier barrel.

Also, do any of you know where to buy parts for Saiga bolts or bolt assemblies. If I use the 12 gauge as the base rifle, I will need a 410 bolt head and extractor.

Any help would be greatly appreciated.