docEE, Good to have you here.
I'll be keen to know how you get on once you try out your new sizing die.
This morning I sent an email to the manufacturer regarding the problem with my full length die so we'll see what happens.
I eventually found a drawing with the case dimensions for 470 and it shows a neck length of .750" With a cartridge length of 3 1/4".
My full length die only produces a neck length of about .600" with the shellholder in full contact with the bottom of the die and the case trimmed to 3 1/4".
Old Kynoch cartridges that I have show a neck length of about .760".
As a matter of interest what is the length of the neck on cases formed in your CH die?