D3,
I don't know about the .45-70 to .450NE, but I sent my
No.1 to Bowen Classic Arms a few months ago to be
rechambered/breeched from .458 mag to .450NE. The price
is pretty reasonable and they have a good reputation for
quality work. I guess I'll find out pretty soon. I was
shooting a DR in .450NE and ended up with a lot of
Bertram brass. Lots of problems with case splits. I ended
up annealing the cases every 3rd shot and then they seem
to hold up fairly well. Huntington Die in Oroville, CA.
sells their private lable HDS cases in a .450 Basic and
these seem to work much better. They also had some of
the older BELL .450 Basic cases. Both were less cost than
the Bertrams and both are reloadable a bunch of times.
I think Bowens web is www.bowenclassicarms.com.
Good luck on your project.
Glen