Update

Have been lurking for a while and been looking for available parts on this side of the pond (Europe)

All aspects taken into account it looks like I am going to build a semi-wildcat based on 8x57IRS and the new caliber is 9,3x57R to be named 57RSE or 57IRS.

web page with simple drawing of the new case

All in all the 45-70 is much more expensive in the long run compared to what I can get hands on as regards need parts for 9,3x57, barrel blanks - reamers - dies - cases - bullets